Make sure your new device is signed into your Apple ID. On the iPhone you can do this by launching Settings from the SpringBoard and tapping Sign in to your iPhone if you're not already signed in.
Make sure you're running the latest software on your device. On the iPhone you can do this by launching Settings from your SpringBoard, selecting General, then Software Update.
Launch the TV app. You may be presented with the offer immediately after launching the app. If not, scroll down in the Watch Now section and tap Try it free.
You should then see a large Enjoy 1 Year Free button. Tap that button, Confirm your subscription, then tap Done.
You can now enjoy your free year of Apple TV+!
Note: After your free year, Apple TV+ will cost $4.99/month in the United States, $5.99/month in Canada.
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