apple tv free for one year, but I cannot activate it, please help me.

What happens when you try to activate the offer?

For reference, here’s how to activate the free offer, and the offer is valid for three months from purchase:

https://offers.appletvapp.apple/

If you’ve followed the Apple activation sequence exactly, contact the folks at Apple and ask for assistance: Get Support

Correct, you had 3 months to redeem the offer.