It's nice to have you in the Community. I'd be delighted to assist you with adding a user.
There should be a green box in the upper right corner of the screen displaying Add user. I've included a brief video to serve as a guide for you:
Should you continue to not see this option, I recommend confirming that Users is selected at the top, since Accountants can provide a slightly different interface. For additional steps on adding or deleting a user, such as modifying access rights, please visit the following link: How to Add, Delete, or Change a User's Access.
I want to ensure that you're able to get the user added, so please feel free to let me know how it goes. If you should have any questions, I'm just a click away. Have a lovely day.