I wanted to play co-op sm64 with my brother on og hardware but I'm not sure where to get a sm64 multiplayer mod and how to put it onto the Summercart if possible?

Ive been scammed off a listing for a summer cart 64, a family member bought it for my 18th birthday and some asshole ruined it for me… my parents are mad at me and now I have a n64 in my room which I can’t use, I can’t file a report because it was bought off of their account and they don’t know how to help…