Rather than write it all out, I've linked to the FAQ in case you need more detailed instructions on how to do one of the steps.
Create a pseud that does not match your username, e.g. if your username is "testy", make a pseud named "pesky"
Download that work in EPUB, MOBI, or AZW3 format and open it in a program like Calibre that will let you see the metadata (HTML and PDF don't get this sort of metadata assigned)
The author name is just the pseud, e.g. "pesky".
The author should be listed in the format "pseud (username)", e.g. "pesky (testy)". This is important because pseuds are not unique – there can be only one user named testy, but everyone could have a pseud named pesky.
For clarity: If the pseud matches the username, only the username needs to be shown.