Under the "Manage users" page from the Gear icon, you should see the "Users" tab and "Accounting firms" tab.
See the screenshot below for reference. You can also invite your Accountant directly from the left Dashboard by selecting My Accountant tab.
Thanks for your reply! Unfortunately, I do not have a "My Accountant" tab in the left, nor it doesn't appear the "Accounting firms" tab in "Manage Users". Please see the screenshots below.
The US version of QuickBooks Online (QBO) has the Users and Accounting firms tabs, franciscodelatorre.
You might have the Global version of QBO based on your screenshots attached. In this version, accountants are added as a Company Admin.
To add an accountant:
You can also refer to this article to know more about adding an accountant in QBO Global.
To learn more about the different user types and levels of access in QBO, refer to this link: User types.
Let us know if you have further questions. We're here to help.