Hi there, @rwbbiz.
You can just invite up to two accountants/accounting firm to have access to your company file in QuickBooks Online (QBO). Please allow me to help share information so you can give access to the newly hired tax accountant.
As mentioned, only two accountants are allowed to be added in QBO, to give access to the new hired accountant, you may delete or remove one of the accountants added. Once done, add the newly hired accountant.
If you don't want to delete/remove the previous accountant added, you may add the newly hired accountant as a company admin. The company admin has the same access as the accountant, but the only difference is, the user can't be added under wholesales and access through the client list (accounting firm).
As a reference about user access and permissions, you can check these articles:
Please don't hesitate to add a comment/post below if you have any other questions about adding user access or accountant access in QBO. I'm always here to lend a helping hand.