You don’t. It’s a little misleading in how it displays for our purpose. The short version is that it’s easiest to say “It’s just a cosmetic oddity, ignore it.” But the longer explanation is that it actually has a deeper purpose that can sometimes play out in more advanced use cases, and would exist whether displayed there or not.
It might make more sense if instead of “firstname.lastname@example.org” it said “email@example.com” because that’s actually what it is, it’s the unix system account that houses your data. Sort of like how each user on a Windows computer has it’s own Documents, Downloads, etc folders in a user folder. That’s your account on our Linux system and it owns all of your files.