Open the Facebook app on your mobile
Tap the menu icon
Go to Settings & privacy
Tap Settings
Tap Accounts Center
Tap Personal details
Tap Account ownership and control
Tap Deactivation or deletion
Select the Facebook account you want to delete
Tap Delete account
Tap Continue
Follow the on-screen instructions
Enter your password if prompted
Confirm the deletion
Check the deletion grace period if shown
Avoid logging in again if you want the deletion to continue