It was tricky both because the website that retrogamecorps linked sometimes didn’t work and there are many variations of the SM64 ROM that all play identically but the website that reads your ROM only works with one particular version. I downloaded several before I found one that worked.
I followed this guide:
https://retrogamecorps.com/2020/12/28/guide-super-mario-64-port-on-rg351p/
It was tricky both because the website that retrogamecorps linked sometimes didn’t work and there are many variations of the SM64 ROM that all play identically but the website that reads your ROM only works with one particular version. I downloaded several before I found one that worked.