1. Navigate to the Microsoft 365 admin center.
2. Click on ‘Teams and groups’ in the left navigation pane.
3. Select 'Shared mailboxes' to view the list of shared mailboxes in Microsoft 365.
4. Select the desired shared mailbox in the list of Exchange Online shared mailboxes. 
5. Click Edit under Members.
6. Click Add Members 
7. Search for the user by name or email address, and click the checkbox next to their name
   • Note: You can add multiple users at a time if needed.
8. Click Add
9. Done! Repeat these steps for any additional mailboxes.