Due to purchase of Apple phone I am entitled to one year free Apple TV . Works fine on computer, but cannot get anywhere setting up on tv (I have Apple TV 3rd genks fine on my computer, but when I try to use on tv with 3rd generation Apple T

If you have an Apple TV (2nd or 3rd generation) and two-factor authentication for your Apple ID, then you may be asked to type your password followed by the six-digit verification code directly into the password field. Additionally, there is a time limit, after which the code becomes invalid.

Try this: First enter the characters of your password (do not submit yet), then manually request a new verification code, then append that code to the password (no spaces or other separating characters), and then submit. That should help you get passed the time limit.