I try to upload anothers person art from itch which is under CC0.

I filled all the fields (except collaborators) and chose that I am not an author but when I press save I get an error/warning that I must specify the author. I meantioned the author in the description and in the Copyright/Attribution Notice sections but I can't find field for specifing author. The only empty field is Collaborators but I can't insert there link to the itch account of the author.... What to do? Where the author field?