How to start the 3 month trial Apple TV+ when purchasing a new Apple TV 4K

I just purchased a new Apple TV 4K. Apparently this purchase allows me to start a free 3 month subscription to Apple TV+. However I can't see how to do that. When I load the Apple TV app on the device it just says to start a 7-day free trial. How do I start my free 3 month subscription that is supposed to come with the purchase of my Apple TV 4K?

Thank you.

-Dave Herrmann