How do I install root certificates?

If you have installed any profile on your own --> Install or remove configuration profiles on iPhone - Apple ...

If you want to turn on SSL trust for that certificate, go to Settings > General > About > Certificate Trust Settings. Under "Enable full trust for root certificates," turn on trust for the certificate. Apple recommends deploying certificates via Apple Configurator or Mobile Device Management (MDM).

Trust manually installed certificate profiles in iOS and iPadOS ...

Please ask Amazon to share their root certificate if they have any.

Amazon is not an Apple product. Contact the app developer here --> App Support or Help - Amazon Customer Service