No sound in YouTube games or Facebook

Hi, download the latest iOS software update, go to Settings > General > Software Update.

Make sure that the volume on your phone is set to the highest.

You can reset all settings, go to Settings > General > Reset > Reset All Settings.

Force restart your phone: Press and hold both the Home and the Top (or Side) buttons until you see the Apple logo.

If the issue persists, you can restore your phone as new:

How to back up your iPhone, iPad, and iPod touch

Restore your iPhone, iPad, or iPod to factory settings