I need to disconnect an apple tv device I used while on vacation

Do you mean sign out for your account on someone else’s device?

• You can remove the device from the list of devices where you are signed in. Then trying to use it there will prompt to sign in again (password). Your email address (Apple ID) may be listed though. Check your Apple ID device list to see where you're signed in - Apple Support
• You can ask the owner to sign out for you. I’m sure it happens with some regularity in e.g. Airbnb situations, hotels, etc.