The offer is no longer for 1 year; it is now 3 months. See: https://offers.appletvapp.apple/tvp01213mf including the instructions below:
Redeem 3 months free of Apple TV+ now.
You can start your 3 months free subscription to Apple TV+ after setting up your new Apple product. Here's how to redeem your offer:
1- Turn on your new Apple device and sign in with your Apple ID.
2- Open the Apple TV app. Make sure your device is running the latest version of iOS, iPadOS, tvOS, or macOS.
3- The offer should be presented immediately after launching the app. If not, go to the Apple TV+ tab where you'll see the offer.
4- Tap Enjoy 3 Months Free.