Add a shared mailbox to Outlook
After your admin has added you as a member of a shared mailbox, close and then restart Outlook. The shared mailbox should automatically display in your Folder pane in Outlook.
What if it didn't work?
If your admin only recently added you to a shared mailbox, it may take a few minutes before the shared mailbox appears. Wait a bit and then close and restart Outlook again.
If that didn't work, then manually add the shared mailbox to Outlook:
Choose the File tab in the ribbon.
Choose Account Settings, then select Account Settings from the menu.
Select the Email tab.
Make sure the correct account is highlighted, then choose Change.
Choose More Settings > Advanced > Add.
Type the shared email address, such as firstname.lastname@example.org.
Choose OK > OK.
Choose Next > Finish > Close.