If you're creating a my.MYOB account and an error appears saying the user already has a my.MYOB account, you can't create another account for the user. Try adding them to MYOB Practice as a staff member by following the To add a staff member procedure. If you have any issues when following the procedure, contact MYOB Support for help adding the user.
Ensure you're a practice administrator or primary contact of the practice. If there are other practice administrators in your practice who have access to the Maintain Users page, ask them to change your account's User Type to Administrator.
If no one else in your practice can access the Maintain Users page in my.MYOB, contact MYOB Support.