Apple requires that all apps allow for user deletion by Jan 31, 2022. (https://developer.apple.com/news/?id=mdkbobfo)
CORE already has this functionality for its Apple TV app, allowing you to have greater control over your personal data.
Steps:
Open "Manage Users"
Highlight the user to remove.
Swipe right to the "X" and select it.
Answer "Yes" to the confirmation prompt.
The account information is wiped from the device.
Once done, if you want to access ATV again (assuming you have an active CORE account in the cloud from your Admin) you would have to start from initial login/setup. None of your prior data is stored on the ATV.