So the real question is, did you purchase from Tesla or third-party? Tesla should have the vehicle released from the system and you should be able to setup the app within a couple days, assuming they didn't make a paperwork mistake or get behind. For third party, you should ask for the prior owner to transfer to you (using the Tesla app), or ask the dealership to ask them. Of course, this might be harder to do. As jz788 says, there are longer ways, but these two are the fastest.