Only the Super Admin can remove or change a Group Manager. There are three ways to do this:
From the Roles & Permissions page: click the Group Manager icon to view the list of current managers; next to each name is an option to Remove Group Manager.
From the Group page: open the All Actions menu and select Change Group Manager to replace them with another team member (who isn’t already managing a group) or select Remove Group Manager to remove them entirely (the group will then be managed by the Super Admin by default).
From the learner’s profile page: go to the All Actions menu and select Remove as group manager.