Select the Accounting firms tab.Then, find the name of the accountant that you want to remove.
Under the Action column, click the drop-down arrow and select Delete.
Click Delete to confirm your selection.
Also, I would like to include the guidelines about managing the accountant users in QuickBooks Online. If you have other users, you can use the audit log to keep track of the transactions that were added, deleted, and modified by them. Here's an article where you can learn on how to use this feature.
You can always post your concerns to this thread. I'll get back to you as soon as I can to help you figure them out. Thanks!