I had to look this up. As far as I know, PhotoGIMP is a patch that enables making GIMP take on some Photoshop appearance.
So that means that you only need to move the files into the appropriate folder.
If you have not already, download the package from git:
git clone https://github.com/Diolinux/PhotoGIMP.git
This will land in your home directory. So you only need to do a basic Change Directory command to enter it
cd PhotoGIMP
Copy the files into your home GIMP config directory:
cp -r .var/app/org.gimp.GIMP/config/GIMP/2.10/* ~/.config/GIMP/2.10/