To do this:
Click the Calendar icon in RDB and then right-click next to My Diary.
Click Sharing and then click Add User or Add user group.
Select User or group to share your diary with and Click OK.
Select the permissions the users need to have.
Click Save and Close.
📌 Note: The person you have shared your diary with, needs to place a tick into the checkbox next to the diaries the user wants to view under Other Diaries.