Car tax / insurance not paid – car canceled – How to re-register?

Hello. An older friend asked me for help. He forgot to pay his car tax and / or insurance for his car (I’m not sure). Then the police came to his home and scratched off the stamp or something. He wants to register the car again and asked me to damti. What do I have to do to register the car again? I’m absolutely clueless. Thank you.