As a group manager, you have total control of each device that has been signed-in to your group. To "add/remove" devices that belong to your member. Please follow these steps:
1.) In your manager account interface, scroll up a little bit to Group Licenses and click the "Manage License Seats" button.
2.) Then, scroll up a little bit to the member's section and click the "Details" button of the member you want to edit.
Then, you will see the remove button to remove a device.
Once removed, you can, however, add it back anytime.
