People have been abusing Facebook, which was a social media revolution, on a daily basis for far too long.

Launch the Facebook app on your iPhone. Tap the profile icon at the bottom right.

Scroll down the menu and access Settings & Privacy→ Settings.  Now, navigate to See more in Accounts Centre.

Go to your user profile and select an account of your preference.  When prompted, tap Username to overview your current username.

Additionally, you can rename your Username if you desire → Press Done.  Finally, press Done to conclude the process.

 Visit the official website of Facebook via any browser of your preference.  Click on your profile → Navigate to the Settings & privacy option from the menu.

Hit Settings when prompted.  In this instance, you can find the Username of your account towards the end of the link, as highlighted below.