@massproduce201 you need to install the retroarch cia from their downloads page. You might even have to copy the retroarch directory structure to the root of your sd card. Not really a retropie question though, so I'd direct you to the libretro forums. They'll have the info you need.
Edit: read this
https://gbatemp.net/threads/retroarch-emulation-thread-nightly-builds-included.400913/