For more information about adding/updating/removing members from a group, please consult this article.
Adding to the Calendar:
Click on the calendar day that this group member goes on call, which will open the event entry screen.
Select the assigned group member, when their on-call starts and when their on-call ends.
Optionally, you can set recurrence, such as repeat every two weeks, until a designated end date.
Updating/Removing from the Calendar:
Click on the calendar event, listing the time and name of the group member on-call.
To update: Modify any of the fields as needed and click "Save". If modifying an event from a recurring series, you will be asked if you want to change just this instance or all following.
To remove: Click "Delete". A confirmation prompt will appear. If deleting an event from a recurring series, you will be asked if you want to delete just this instance or all following.