This is not going to be an easy fix for a novice. You might get lucky and find a broken wire but you really need to run through a process of trouble shooting. First and foremost check the batteries on the CPU board is there any acid leakage? If so the simple thing for a novice is to replace the board. If no leakage follow the manual for testing switches and the mini playfield tests.
Hard to walk you through this online you may consider posting here to see if someone is willing to come over and take a look at it.
It’s certainly reparable you just need someone with experience to assist you.