how do I use app specific passwords to log in to appleTV

You wouldn't use an app-specific password for that. See the following from Using app-specific passwords - Apple Support

App-specific passwords are passwords for your Apple ID that let you sign in to your account and securely access the information that you store in iCloud from a third-party app. For example, use app-specific passwords with mail, contacts, and calendar services not provided by Apple.

If you have two-factor authentication turned on, see the following from Two-factor authentication for Apple ID - Apple Support

If you use two-factor authentication with devices running older OS versions—like an Apple TV (2nd or 3rd generation)—you might be asked to add your six-digit verification code to the end of your password when signing in. Get your verification code from a trusted device running iOS 9 and later or OS X El Capitan and later, or have it sent to your trusted phone number. Then type your password followed by the six-digit verification code directly into the password field.