Hey deanre1,
Welcome to Apple Support Communities.
We recommend making sure the Apple TV software is up-to-date by following the steps below:
1. Go to Settings > System > Software Updates and select Update Software.
2. If there's an update, select Download and Install.
3. Wait for your Apple TV to download the update. Keep your Apple TV connected and plugged in to power until the update is complete.
Since updates include fixes, it's a great idea to keep all devices up-to-date. You can access the steps in this article as well: Update your Apple TV.
If updating the Apple TV doesn't help, and you're not experiencing issues with any other apps on the Apple TV, we suggest contacting Amazon support here: Help & Contact Us - Amazon Customer Service. There may be a setting that needs to be configured in order to access the app on the Apple TV.
Best wishes.