You can control who has access to CloudFiler via the Microsoft 365 admin center.

In a browser, navigate to the Admin center

In the left-hand menu select Settings and then Integrated Apps

Select CloudFiler from the list and then in the box that appears on the right, select Edit users

You can then add people by name or by group. 

WARNING: It can take up to 24 hours or more for Microsoft's servers to register any change. This applies to both enabling and removing the Add-in.