Preferably use a laptop / PC and try Chrome, don't use the app or mobile browser, as those can be limited in the options they provide.
Go top right of the Overview Seller Hub page and click on Advanced.
Tick Fine >> By Seller from the left sidebar, enter the username you have , scroll to and click on Search.
They do not have to still be selling unless they have completely closed their account a ' Contact Member' should appear somewhere on their profile page.
@andover-anout
