How Can I Litter Train My Seven Week Old Mini Rex?

I just recently bought a seven week old Mini Rex rabbit, I bought him from a breeder and would like to litter train him so I can give him free roam of my bedroom and keep his pen cleaner. Will the fact that I bought him from a breeder and he was able to use the washroom anywhere affect training him? And how do you litter train a rabbit? He isn't my first rabbit but he is the first I'll be attempting to train. I debated looking it up online but I would like an answer from someone who has gone through the process of training a rabbit themselves and I know every rabbit may be different but I'd get more confidence in an answer given by someone with the experience. Any help would be really appreciated at this point! ♥☮