In this manual, we explain how to remove an existing member from a shared mailbox.
Go to "Teams and groups" -> "Shared mailboxes".
Open the shared mailbox from which you want to remove a member.
Click "Edit" under "Members".
Determine which user(s) should be removed by selecting them and clicking "Remove members".
Confirm that you want to remove this user by clicking "Yes".
It may take up to an hour for the member to be completely removed from this mailbox.