All Mobile Phone Apps like Facebook or Gmail have their own notification sounds but you can easily change these if you want to. We'll show you an example with WhatsApp notification tones:
1. Open the WhatsApp
2. Click on the three dots to open the menu on the top right of the screen
3. Tap on Settings
4. Then go to Notifications Tone.
Now a list of different ringtones will open. Select your favorite ringtone then confirm your favorite by tapping OK.