To add a user as an administrator of your wiki, visit Special:UserRights on your wiki. For instance, if your wiki ID is goodreads, you would visit https://goodreads.mywikis.net/wiki/Special:UserRights to manage their user rights.
Your account needs to have bureaucrat rights in order to manage user rights on Special:UserRights. To check the list of bureaucrats, or to check what user rights you have, visit Special:ListUsers on your wiki.
When adding someone as an administrator, don't forget to add them as a bureaucrat as well if you want to let them change user rights as well.
If you're the owner of your wiki and don't have administrator or bureaucrat access on your wiki, open a support ticket and our support team will be glad to assist you.