A
Here are the instructions as of June 16, 2018:
- Open the Facebook app
- Click the icon with the three bars in the top right-hand corner of the screen
- Scroll down and click on "Settings & Privacy"
- Click on "Settings"
- Scroll down to "Notifications" and click on "Notification Settings"
- Scroll down to "Where You Receive Notifications", then click on "Push"
- Click on "Tone". It has a Phone icon next to it
- Choose the sound you want