How can I restrict user groups so they can access only their office?

Login in an admin in Apollo.

Navigate to Setting >> Manage Groups.

Click on edit icon under action.

Uncheck "Access all Office" so this group will only see the patients pertaining to their office.

The selection of office can be done in Manage clinicians.

Check "Access all Office" if you want the group to have access to all the patients irrespective of their office.