Procedures in the event of a driver’s flight

Hello @ All, I give my girlfriend my car, because at the moment I prefer to ride a bike, I can go to school with her. Actually I always got a bit of a shot, because I’ve often heard that something happened in the parking lot there (park-wimpler, car broke open, etc.) When I passed my car the day before yesterday, I saw that my bumper is no longer properly in the front of the bracket, is torn in one place and the color bursts under the headlight. My girlfriend didn’t know where that came from either. Abetr said that must have happened in the parking lot. She could also remember the car that was parked in front of her. Yesterday someone also approached her, who, with those who went into a class that drove in her. Only after a long time he admitted it. But he thought it was his father’s car and he had no insurance because he didn’t need it. How should he sue him. D I’ll do it, too. But how am I going to proceed now to get to my right? CU Jens