Developer Options 

Newer Fire Tv devices do not have "Developer Options" enabled out of the box. The developer options can be found in the settings area as a menu item. If you do not see it there that means that they have not been enabled on your device.

To Enable "Developer Options"

There is a slight variation in the steps depending on whether you have an Amazon device, such as the Fire TV Stick, or a Fire OS-powered TV. Differences will be highlighted where they occur.

1. On your Fire TV's home screen, select the gear icon to open Settings.
2. Select My Fire TV.
3. Select About.
4. Highlight the first option in the list. This should be a reference to your specific device, i.e. you can see your Fire TV device’s name under this section.
5. Press the remote as if you were selecting this item seven times.
6. If everything goes right, you should see a message confirming you're already a developer.
7. Press the back button on the remote to go back to the previous menu.

If you're using a Fire OS television, then step 2 may refer to Device & Software instead, but the rest of the steps are the same. On completing the steps you'll now see the missing Developer Options menu.

The Downloader 

set up the Downloader app on your Fire TV Stick.

1. Go to your Amazon Fire TV Stick home screen and click the Find symbol.
2. Click Search.
3. Type Downloader on the search page, then click Downloader from the displayed results.
4. Click on the Downloader tile.
5. Click Download or Get, depending on the option displayed on your screen.
6. Wait for the Downloader app to complete the download and installation. DO NOT open the Downloader app yet. You can use it only after granting it sideloading permission.

Adding Third-Party Apps

1. Click the Settings icon on your Fire TV home screen menu bar.
2. Click the My Fire TV tile at the bottom-left corner.
3. Click Developer Options in the middle panel.
4. Ensure ADB Debugging is On, then click Install Unknown Apps. If your device shows the option Apps from Unknown Sources instead, click on it to turn it On.
5. If shown, Click the Downloader option to turn it On.