You have 2 options in this situation, and this depends on the type of Intuit account your accountant has.
If they a QuickBooks Online Accountant (QBOA) account, then you can invite them as an accountant user. Ensure you're logged in as the master administrator so you can send out the invite.
If they have a QuickBooks Online (QBO) account, you can invite them as a company admin instead.
Follow these steps:
If they don't have an Intuit account, once they accept your invitation they'll be routed to the correct page where they can create the necessary account (either QBO or QBOA).
Check out this article to learn more about how many users you can add to your account, depending on the version you have: How many users can I set up?
Feel free to leave a comment below, in case you need further assistance. I'll be sure to get back to you.