How to merge CommCare user group

Recently, two user groups with same name(with differences in alphabet case) were mistakenly created. The two groups contained the same set of of usernames. One was deleted when flagged but some rcords had been attached to the user group and are not showing up in the follow-up case search.

I can restore the deleted user group but how do I merge it with the other one? I'm open to other suggestions on how to resolve the stated issue.