Fixing a superadmin deletion problem

I am the owner of a multisite WP site, with the first actual site almost ready to launch. I parted ways with my original webmaster and superadmin. He was removed from the system by me. Then my new webmaster accepted my email invite to be an Admin and then made himself a superadmin. Then he decided he was too busy to continue working for me, so I removed him — as the only superadmin.
Now my new (real) webmaster has become an Admin and has access via my hosting company (GoDaddy — dedicated server) to the FTP files, but cannot make himself a superadmin in WP — meaning he cannot do any work on the backend of the site. I am also an admin, but I see no way to make the new webmaster/admin a superadmin. Can someone please send me instructions on how to resolve this? I am keeping my fingers crossed there is a fix. Thanks.