How do you add an administrator

Problem/Motivation

While modifying group permissions, the permissions for Group Administrator were inadvertently removed (the check box) from the user.

There is now no group member identified as group administrator. Due to Groups 2.x security, no Site Administrator can access the group.

So, the question is - how do we get one of the group members back as group administrator when we have no way to access the group?

TIA, Mark