Please note usernames are only for people who are under 13. Usernames can't be changed. Display names are for people who want to do anything public on a BBC website or app. Display names show when you're signed in on the website or on the BBC iPlayer or BBC Sounds app on your TV. Display names can be changed in your BBC account settings on the website.
Check out the guidance below as you may be able to fix the problem yourself right now:
What’s the difference between a username and a display name?