You can grab the file for Google app for Android TV v3.0 (Arm) from APK Mirror and sideload it on your Android TV. Source: +Artem Russakovskii ...

Sometimes, not every Android app will be available on the Google Play Store in your region, which means you'll need to install the APK file instead.

The APK file format is used to distribute applications to Android devices. Many APKs are available through the Android Market. Others are available through third party websites. APKs not ...

To do so, first, sideload Aptoide APK on your Android TV (be it Mi Box or any other Android TV) as mentioned above. Once Aptoide is installed, launch it and look for Prime Video in it.