Extract and copy the RetroArch folder to '/data/homebrew/'
Add the BIOS files to '/data/homebrew/RetroArch/.config/retroarch/system/ '(Not included; you can use the ones from Batocera).
Copy your ROM backups to /mnt/usb0/roms/ (e.g., /mnt/usb0/roms/nes/). Read the guide!.