You may have a scenario where you do not want to give access to a Dynamics 365 instance to certain users. One way to do this is to use security groups in Office 365. To do this, create a security group and add administrators and members.
Then, in the Dynamics 365 Administration Center, select to edit your instance:
Scroll down to Security Group:
Select the security group you want to use:
Press Save and that’s it. Your instance will now be restricted.