If you are a user of Funimation and want to activate your Apple TV, then follow the below-given steps:
First of all, Open the Settings app on your Apple TV.
Then, go to the options of Accounts & Passwords of your Apple TV.
Choose the option of Sign In with Apple ID from the given displayed list.
At last, You will be required to enter your Apple ID-related details to sign in to your account on the Apple TV.

Follow above mentioned steps to activate your Funimate account in Apple TV.

Read more here:- https://www.allneedy.com/funimation-com-activate/