This will guide you through adding a shared mailbox to your personal account in Outlook 365.
\uD83D\uDCD8 Instructions
Follow the steps to add a shared mailbox in Outlook 365
Click the File tab in the top left corner.
Click Account Settings and then Account Name and Sync Settings
Click on More Settings
Go to the Advanced tab and press Add…
Enter the name of the mailbox and press ok
Remove the check mark from “Download shared folders”
Press Apply and restart Outlook.
The mailbox will now appear in the left pane under your personal mail.