Removing a group from a shared mailbox

[finsfree]

A user has left our organization and that user's mailbox was converted into a "shared mailbox". Because the user was a member of the "sales" group now the shared mailbox is a member of sales as well.

How can I remove the sales group from this shared mailbox? There is NO options in the Microsoft 365 admin center. 

Next time the groups will be removed before converting in to a shared mailbox...

[#2]

You should be able to remove it via PowerShell, but since you haven't specified the group type I cannot give you the exact cmdlet.