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:
    • Open 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 info@contoso.com.
    • Choose OK > OK.
    • Choose Next > Finish > Close.


Source:

https://support.office.com/en-us/article/open-and-use-a-shared-mailbox-in-outlook-2016-and-outlook-2013-d94a8e9e-21f1-4240-808b-de9c9c088afd