Change Apple ID in Apple TV app on Mac

Hi, so my MacBook is signed into apple tv under my exes apple id, how can I change it back to mine? If possible, without having to contact him.

To be more specific, when I click on AppleTV on my mac, it always says his name, and I still have access to all the movies and such that he bought. I would like to sign out of his account, and sign into mine. I would really like to be able to do this without having to contact him, since we've been no contact for 2 months now. However, I'd really like to access my own AppleTV account.

Thank you!