Guide to adding shared mailboxes in Outlook app: iOS
Step 1: Open the sidebar by either selecting the icon to the left of the word Inbox in upper left section or swiping right from the left edge of the app.
Step 2: Select the gear icon.
Step 3: Select Accounts.
Step 4: Select Add Account.
Step 5: Select Shared Mailbox.
Step 6: Enter the name of the mailbox you wish to open and select Add Shared Mailbox.
Step 7: Select the back arrow, follow by the X icon in the upper left corner.
Step 8: Open the sidebar again to see your new account listed on the left side. Select the account to access your shared mailbox contents.