There is no way to resign with a CPU team. Having said that you can simply wait for the new season to start, request contracts and get one.
Side Note: This is exactly why the CPU teams should have forums, this guy has been playing the game for 3 seasons and has never been anywhere but a CPU team. The FAQ in the forum is counter intuitive for new players to find and user experience needs to improve to expand the "non-geek" user base , just like this guy.