If your tax agent has a QuickBooks Online for Accountant file, you can invite them to your QuickBooks Online account as an accountant user. Here's how to:
From your QBO account, click on Settings icon.
Click on Manage Users.
Click on Accountants tab.
Enter your accountants email address.
Select Invite.
Your accountant will receive an email about the invite and they need to accept the invite. If they don't have an accountant file they'll be asked to sign up for QBO for Accountant file.