Hi @Afolayan_Favour and welcome to the community 
This seems to be related to Autocomplete default username (+random password) when creating new entries (or option in generator) with the using default username being a separate feature request.
Here is a previous thread with some more information and links to old Pull Requests showing a possible approach.
To get started please have a look at our Contributing Guidelines. These will have everything you’ll need to get your environment set-up.
Kind regards,
Daniel