Create button on-screen controls to move car

Hello! I’ve got a decent car game going so far and I want to add touch controls. All the online tutorials try to make their own physics engine, but I want to keep the carcontroller.cs that came with Unity. Basically, how do I add touch controls to move my car WITHOUT changing physics? Thank you!

I, uh, don’t think that they are making physics engines. Which tutorials were they?