What is your model Apple TV box? Identify your Apple TV model - Apple Support
On Apple TV (3rd generation), the Prime Video app should be pre-installed with system software 7.2.2 or later.
On Apple TV (4th generation or later), the Prime Video app is available from the on-device App Store with system software 14.3 or later. Find apps in the Apple TV App Store - Apple Support
When you launch the app, you are asked to sign in using your Amazon account. (You don’t actually have to enter credentials on Apple TV.) Click ‘Sign In’.
Next, you are asked to link the ‘new’ device to your account, either using a web code or using a QR code. Choose one and do as instructed. This step must be done only once (unless you reset).
Next, you are greeted with the Profiles page, to allow for differentiating between several users. Select one and continue. (You will see this page each launch.) Enjoy.
