In the Nick Jr. App, go to the Settings tab. Under TV provider, click Sign In.

Select your provider from the list. You will be shown an activation code. Using a browser on a computer or mobile device, visit the Nick Jr. activation page and enter the code that is provided. If this doesn’t work, turn on third-party cookies in the browser’s settings and try again.

You will be redirected to your TV provider’s sign-in page. Enter your username and password. Once you have logged in, the Nick Jr. App on your Apple TV will show a successful sign-in message!