So, your Fire TV remote could control devices like your cable box, soundbar, and more, turning them on, controlling volume, and more.  

If  you are experiencing a no sound issue   
Solution :

1 . Disable HDMI CEC, go to Fire TV Settings > Display and Sounds > HDMI CEC Device disable. 

2. RestRestart your device. 

Watch this video for more details.

3. If all else fails, uninstall the app with the no-sound issue and reinstall it. 

If the above does not work or if other apps have sound: 

1. Got o Firestick Applications

2. Manage Install Application

3. Uninstall / remove the App

4. Open the Downloader app, look in the files section on the left of the screen

5. Look in File you should already have the app downloaded, click it

6. Install the app and login.