First activate the free trial. See below
This can be done after you’ve set up your new phone and signed into it with your Apple ID.
If your Apple TV has the TV App it can be activated on that , so long as your signed in with the same Apple ID you set your phone up with.
Here’s how to redeem it:
Turn on your new Apple device and sign in with your Apple ID.
Open the Apple TV app. Make sure your device is running the latest version of iOS, iPadOS, tvOS, or macOS.
The offer should be presented immediately after launching the app. If not, go to the Apple TV+ channel page where you’ll see the offer.
Tap Enjoy 1 Year Free.
Apple TV + Offer
https://support.apple.com/en-us/HT210573