Welcome to the Apple Community.
On your new device, sign in with your Apple ID account during the setup process or at a later date in the Settings.
Use the Software Update feature to check whether your device is running the latest version of its operating system. If not, download and install the update when prompted to do so.
Now open the TV app on your device and select the Watch Now tab.
The offer should be presented immediately after launching the app. If not, scroll down until it appears and select the button labeled with the text “Enjoy 1 Year Free”.
If you still don’t succeed contact Apple TV Support