Guest without name option "question without registration"

[Edjazoli]

Hi, any chance that someone will tell me what I need to change in my theme that I will end up with, instead of putting guest name, only with ..."by guest"

Check pic below for visualisation LOL.

I realised as well ig guest will chose they name for topic his/her is unable later one choose this same name prior the registration as message " this name is already chosen" appears.