Newbie for you; inexperience describes me. Desktop is the next tab over from 'themes'. My 'express' notation gives brief landmarks for you to look for, and hpoefully arrive where the action happens.
Personally I have never called a web page for an alternative desktop. The o24 url is not a valid link from my computer. Selecting this from the list should give the option to delete.
Since there is no file on the computer for this desktop, HJT will also accomplish the same.
Scan with HJT > tick the O24 entry > Fix selected.