How do I edit a Username

[appteam6]

I invited user to my app but some of them do not have a username. Just there email address. So when they are submitting data and it records username() it shows blank. I cannot seem to find anywhere to add a name to that useremail. Can anyone help with this please.

[Bellave_Jayaram]

USERNAME() doesn’t always work so you should use USEREMAIL() instead.