If you want to increase the storage on your Amazon 4K Firestick (Any Fire Device that support OTG), then follow the steps below
- OTG Cable
- USB 3 Flash drive
Connect the OTG to your device and plug in your USB drive.
(APK at the bottom of the page)
1. From the Main Menu scroll to hover over Settings.
2. Click My Fire TV.
3. Choose Developer Options.
4. Click Apps from Unknown Sources.
5. Choose Turn On.
6. Go to About — Network and confirm your IP Addresss
Install the APK from the link below