For Shared Mailboxes, to release quarantined email you need to do this through Outlook on the web.
Step by Step guide
Visit https://outlook.office.com/ and login as normal.
In the top-right, click on your initials, and at the bottom of the menu choose "Open another mailbox"
Start typing the mailbox you want to access, and click it
You should now have full access to the mailbox through the web:
Finally, you will be able to find the Microsoft "Spam Notification" email and choose to block, review, or release the relevant prevented email.