Players are each allowed 1 username change. If you would like to change your Username:
1. Tap Profile button
2. Tap your Avatar icon at the top of your Profile
3. Delete your Username from the Username field and type in your desired Username
4. Scroll to the bottom of the screen and tap Save Changes
If the username change is accepted, your username is immediately changed in your account.
Once you change your username, the Change Username functionality will no longer be available so make sure to select a username that you wish to stick with.
If you don't see the Change Username functionality in Profile, you have already changed the username in the past and cannot make an additional username change.
Player Services does not have the ability to change a Username so the player must initiate the username change following the instructions above.