Primary site - multiple domains

How can my primary site have multiple domains?

I've got several domains that I use for multi-site: gracesites.com, harvell.design, cofc.site... These are set up so that customers can use them as sub domains.... but if you go to http://www.cofc.site or gracesites.com it redirects to a sign up page....

http://harvell.design/wp-signup.php?new=gracesites.com

How can i make these domains just redirect to harvell.design?