Apple TV 3rd gen can not input 2 factor passcode,please help i can’ t add ID

Get a verification code and then start signing in; when it asks for yur password, enter it followed by the verification code (both in the same password box)

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.

If you continue to have a problem please call AppleCare. YThey can give you a hand.