Hey Joey,
Great question. Let me help you out with this one.
Joey, you can leave a Pro League up to 72 hours before the draft takes place and get a credit that you can use to create a new team. Just follow the steps outlined in this help article:
Deleting a Fantasy team
If you're past the 72-hour window, but the league doesn't fill before the draft begins, then this Help article will explain what happens from there
Pro Leagues that do not fill
I hope this explains what your options are at this point. If not, be sure to reply to this thread so we can help you further.
Good luck this season!