Enable Unknown Sources
To install app stores that are not initially present on your device, Android requires you to enable the Unknown Sources setting. This allows you to download apps and games from sources other than Google to your mobile device.
Note: Any time you're using the Internet, you should take care to download content only from sources that you know (such as Amazon). Amazon only downloads apps and games that you've intentionally purchased to your device.
To enable the Unknown Sources setting:
Amazon Appstore for Android App:
During the installation process for Amazon Appstore, follow the on-screen prompts to enable Unknown Sources.
To access the Unknown Sources setting directly, press the menu icon or button from the Home screen and tap Settings. Select Security (Android OS 4.0+) or Applications (Android OS 3.0 and earlier). You may need to scroll down to see the Unknown Sources setting. For Android 8.0+, tap Settings, then tap Apps. Next, select "Amazon App Store," then tap Install unknown apps and toggle "Allow from this source."