Follow the simple steps below to enable ADB on your Fire TV device.
Note: This guide is for Fire TV OS version 22.214.171.124 and newer. See this guide for older OS versions.
While on the home screen scroll right to Settings.
Scroll to the right then select Device.
With the Device dialog open select Developer options.
Turn ADB debugging and Apps from Unknown Sources to ON.
ADB Debugging is now enabled on your Fire TV or Fire TV Stick. Your Fire TV is now setup to allow side-loading .apk files.