Currently working only on FireOS 7 (newest models)
Take control of volume level in fire stick tv device.
Not compatible with HDMI CEC (TV, projector, ..., control)
Be able to increase and decrease volume level of the device in a simple and easy way.
- Make sure to your mobile phone and firestick tv are in the same network
- Allow developer mode in the firestick tv and enable remote debugging
- Open the app and fill the ip address (get it on network details on your fire stick)
- Click on connect
- A notification should appear on the tv asking for permissions. Check on "always trust this device" and continue
- Increase/Decrease the volume at will

Enjoy!

How to get the ip address?
From the Home screen navigate to Settings and click Ok.
Now, scroll over to My Fire TV and click on it .
Next, click on About.
Then, scroll down to the Network option and click on it. That's all there is to it. You'll see the IP address on the right side of the screen.
After a successful connection, the ip will kept in the box dropdown, no need to re enter it every time.