1 - Log in to the Control Panel. More information on this can be foundĀ here.

2 - Click on Manage next to your Domain Name

3 - Click on Mailboxes

4 - Click on the Room Mailbox. In this case, Events

5 - Click on Calendar Permissions

6 - Click on Add Permissions

7 - Select and move the relevant Users or Groups

8 - Apply appropriate pemissions and click save

9 - Finally you will see the permission added