To install third-party apps (such as APK files), you must first enable Developer Options on your Fire TV Stick. This unlocks the ability to allow app installations from outside the Amazon Appstore.
Developer Options is hidden by default on newer Firestick models, so you will need to reveal it before continuing. Once enabled, you can turn on the setting required for sideloading apps.
Follow the steps below to enable Developer Options before installing any external applications.
Step 1
Hover over the Settings icon and click My Fire TV.

Step 2
Click About. (This is typically where you would find Developer Options)

Step 3
Hover over Fire TV or whatever your device is and click the OK button on your remote 7 times to become a developer.
You will then encounter a message at the bottom of your screen stating “No need, you are already a developer.”

Step 4
Click the back button on your remote and you will notice Developer Options is now showing within My Fire TV

Step 5
Click install unknown apps

Step 1
Then make sure it says ON, under Downloader

Now you are properly prepared to start installing apps!
