I guess, you can start with Conor’s PID tutorial: VEXCode PID Tutorial
Then, you can look at more PID references: PID course/tutorial - #4 by _Colossus
The code itself is going to be straight forward - you can copy it from one of the examples and use IMU accelerometer tilt as your input. It is tuning of PID coefficients that is going to be challenging. Robot with the platform are going to have so much inertia that you will need robust calculation of derivative to make it settles fast and reliable.