Please understand that "coppermine for e107" is a user contribution that is not "officially" supported on this site. The devs and supporters on coppermine.sourceforge.net have not experience with the e107 port, so things might be different with the e107 port. Anyway, in standalone coppermine, the admin can create users with the admin menu "users", button "create new user" and choose from the dropdown field "User group" administrator. He can also modify existing users to become admins the same way. If you don't have these options in your menu, my advice is to ask for support on the e107 support board or contact the author of the port.
GauGau