Hello,
After approve Super User you lost it status. I mean you move super user in other group.
You need recover admin password and username following below documentation
docs.joomla.org/How_do_you_recover_or_re...ur_admin_password%3F
Before activated superuser account you need Synchronize Joomla Users with Simple Membership
ordasoft.com/News/Other-Joomla-Extension...mple-membership.html
Thanks
Taras