Hi Jevannet,
Thanks for you update.
To remove a shared mailbox, you may sign in MOP (Microsoft Online Portal) using your admin account, on Admin page, select Users under Management, you could delete the shared mailbox.
Then you may create a user mailbox (not a shared mailbox and recommend you use a name different from the shared mailbox you have deleted) as usually, then grant full permission to the users you want of the new user mailbox.
Thanks,
Eric Sun
Thanks for you update.
To remove a shared mailbox, you may sign in MOP (Microsoft Online Portal) using your admin account, on Admin page, select Users under Management, you could delete the shared mailbox.
Then you may create a user mailbox (not a shared mailbox and recommend you use a name different from the shared mailbox you have deleted) as usually, then grant full permission to the users you want of the new user mailbox.
Thanks,
Eric Sun