Enter your accountant's email and then select Invite.
To add a new one, click on Invite.
Enter your accountant's info, then select Save.
Once done, QuickBooks sends an email invite to your accountant. The email has steps on how to connect your accounts. If your accountant doesn't have QuickBooks Online Accountant, there's also a link for them to sign up.
For more information about the different user types and levels of access in QuickBooks Online, I suggest browsing this article: User Types and Permissions.
In case you don't want your accountant to access your books anymore, you can remove them. I'll guide you how:
From the Gear icon, select Manage users.
Select the Accounting firms tab.
Find the accountant you want to remove.
Click the small arrow drop-down arrow under the Action column and then choose Delete.
Select Delete to confirm.
I'll be around if you need anything else. Feel free to click the Reply button. This way, I'll be able to assist you immediately.