https://github.com/gobabygocarswithjoysticks/car-code
Github for the website code: https://github.com/gobabygocarswithjoysticks/programmer
The new standard code is in this directory: https://github.com/gobabygocarswithjoysticks/car-code/tree/main/gbg_program (you can edit and upload it yourself using the Arduino IDE).
Instructions for modifying go baby go cars to use this code can be found here: https://gobabygocarswithjoysticks.github.io/index/