If you want to create a WindowsPE execution environment that boots from a CD/USB flash drive and automatically launches the erase program, you need to use the method described in "Building WindowsPE boot environment" below.
However, if you want to start the erase program and erase manually in a Windows PE environment, you can do it easily by following the steps below.

Create "System Repair disc" on Windows10/11

This can be done from "Control Panel" -> "Backup and Restore".
Please see the Windows manual for detailed instructions.

Boot your PC with the "System Repair Disc"

・After booting with the "System Repair Disc", select "Command Prompt" from the screen.
・Replace the "System Repair disc" with a CD containing the Windows erasure program "gppro4.exe", or insert a USB flash drive containing "gppro4.exe".
・Run "gppro4.exe" from the CD or USB flash drive at "Command Prompt".

 * Normally, the drive assignments is as shown below. However, depending on the system.

  X: Windows system deployed in memory
  C: Internal disk drive 　
  D:,E:,F:　etc.  CD drives, USB flash drives, etc.

Example:
If the USB flash is the D: drive and "gppro4.exe" is in the root folder of the USB flash drive, enter the following to start it.

D:\gppro4.exe

Building WindowsPE boot environment

In order to use the "Windows Erase Program" (gppro4.exe) in a WindowsPE environment, you must create the WindowsPE environment yourself.
Below are the steps for the latest version (10.0.226.21.1) as of August 2023.
For other versions, the steps may be different.  

Note on WindowsPE

WindowsPE is an OS that is highly compatible with Windows and is provided free of charge by Microsoft, but it is for temporary use, including disk erasure.
Therefore, if continuous use exceeds 72 hours, it is designed to automatically stop. Please be careful when erasing large size disks.
Please see Microsoft's website for details.

Download/install WindowsPE environment

Download
Download "Windows ADK for WindowsXX" and "Windows PE Add-on" from the Microsoft site.

Install ADK, WindowsPE Add-on
When installing "Windows ADK", it is necessary to enable [Deployment tool] feature.
*Even if all other options are OFF, it will still work for this purpose only.
After installing "Windows ADK", install "WindowsPE Add-on". 

Creating a base WinPE image

Run "Deployment and Imaging Tools Environment"
From start menu, find [Windows Kits]->[Deployment and Imaging Tools Environment], run it as Administrator.

Create base WinPE image
At the [Deployment and Imaging Tools Environment] command prompt, run the following command.
The files required to run WindowsPE will be created under the specified folder.

copype amd64 C:\WinPE_amd64

amd64: Specifies the construction of a 64-bit environment.
Windows PE equivalent to Windows 11 only provides a 64-bit environment.
*When building in a 32-bit environment with an earlier version, it will be "x86".

"C:\WinPE_amd64": Created under this folder. Any folder can be specified.
*This folder name will be used in the following explanation.

Configure WinPE image and embed the program

Run "Deployment and Imaging Tools Environment"
From start menu, find [Windows Kits]->[Deployment and Imaging Tools Environment], run it as Administrator.

Mounting WinPE boot disk image file
At the [Deployment and Imaging Tools Environment] command prompt, run the following command.
By mounting, the contents of the boot disk image file [boot.wim] can be accessed under the [mount] folder.

Dism /Mount-Image /ImageFile:"C:\WinPE_amd64\media\sources\boot.wim" /index:1 /MountDir:"C:\WinPE_amd64\mount"

Adding required packages and drivers
At the [Deployment and Imaging Tools Environment] command prompt, run the following command.
Add the necessary packages to run "gppro4.exe".

*In the standard state, disk drivers and network drivers for general desktop and notebook PCs are included, but if you need additional drivers for servers etc., install them here.

required package
・WMI WinPE-WMI.cab

Dism /image:C:\winPE_amd64\mount /add-package /packagepath:"C:\Program Files (x86)\Windows Kits\10\Assessment and Deployment Kit\Windows Preinstallation Environment\amd64\WinPE_OCs\WinPE-WMI.cab"

If you need to add drivers.

Dism /Add-Driver /Image:"C:\WinPE_amd64\mount" /Driver:"C:\SampleDriver\driver.inf"

Specify the required driver file (*.inf) in the "C:\SampleDriver\driver.inf" part.

Time zone and keyboard settings
At the [Deployment and Imaging Tools Environment] command prompt, run the following command.

Dism /image:C:\winPE_amd64J\mount /Set-Timezone:<Time zone name> Dism /image:C:\winPE_amd64J\mount /Set-InputLocale:<input_locale>:<keyboard_layout>

You can check the current timezone and locale:keyboard settings using the following command.

Dism /Image:"C:\WinPE_amd64\mount" /Get-intl

The timezone and locale:keyboard_layout values that should be set can be obtained from the PC currently used for configuration using the following method.
*"/online" indicates the currently running Windows,
and "/image" indicates the specified Windows image file.

If you want to set it up like in the example above, run the following command.

Dism /image:C:\winPE_amd64\mount /Set-Timezone:"Eastern Standard Time" Dism /image:C:\winPE_amd64\mount /Set-InputLocale:0409:00000409

Embedding "gppro4.exe"
Perform the steps below with the boot disk image file [boot.wim] mounted.

"C:\WinPE_amd64\mount\program files"

Copy the following to this folder. (Copy with regular Windows Explorer)

gppro4.exe : "Windows Erase program". For 64bit WindowsPE, use the 64bit version "gppro4.exe".
config.gp4 : Configuration file created using the "Startup Environment Creation Tool"/"Creating WindowsPE configuration File". (Copy required only if used)
license.gp4 : License file required when using "gppro4.exe"

Settings for automatic execution of the program ("gppro4.exe")
Perform the steps below with the boot disk image file [boot.wim] mounted.

"C:\WinPE_amd64\mount\Windows\System32"

Create a text file named "Winpeshl.ini" in this folder.
Write the following as the contents of the file.
*Please be careful not to add ".txt" etc. to the end of the file name.

[LaunchApps] startnet.cmd "%systemdrive%\Program Files\gppro4.exe" wpeutil shutdown

Unmounting WinPE boot disk image file
At the [Deployment and Imaging Tools Environment] command prompt, run the following command.

Dism /unmount-image /mountdir:C:\WinPE_amd64\mount /commit

If you change the contents of the boot disk image file [boot.wim], be sure to unmount and close the boot disk image file.
Before unmounting, please make sure that no other program is accessing the folder under "mount".
It is also not possible to open the folder in Explorer.

If an error occurs when unmounting, please do the following command.
In that case, mount it again and check the contents.

Dism /unmount-image /mountdir:C:\WinPE_amd64\mount /discard

Creating a bootable CD image file, configuring a bootable USB flash drive

CD Image file
At the [Deployment and Imaging Tools Environment] command prompt, run the following command.
*WinPE boot disk image file must be UNmounted.

MakeWinPEMedia /ISO C:\WinPE_amd64 "C:\anyfolder\WinPE_amd64.iso"

Here, "c:\anyfolder\WinPE_amd64.iso" is the output CD image file name. Please specify any file.
Create a CD-R from the created ISO file. See "How to create a CD from an image file".

USB flash drive
At the [Deployment and Imaging Tools Environment] command prompt, run the following command.
*WinPE boot disk image file must be UNmounted.

MakeWinPEMedia /UFD C:\WinPE_amd64 X:

Here, replace "X:" with the drive letter of the USB flash drive to be written.