In this context, "fiddling" means to play with something. Usually it means someone is using their hands or fingers to manipulate an object or play with an object, like a toy or a puzzle, or a switch on an electronic device. (A fiddle is also a type of musical instrument, like a violin, but that does not matter here.)

Hello! In this instance "fiddling" means to change settings or make adjustments to the high-tech gadgets found in the cars. This is often to see how they work properly or to see discover all their functions.

https://www.lexico.com/definition/fiddle 1(no object) Touch or fidget with something in a restless or nervous way. ‘Lena fiddled with her cup’ It's the definition in Lexico. Drivers just can't resist touching it, pressing some buttons, or turning it over and over because it's high tech.