You can sign up for QuickBooks Online Accountant to find the ProAdvisor tab, rohwonjin18. I'll elaborate on this in detail below.
You'll need to create a QuickBooks Online Accountant, which I agree with @Chrea. This is where you can access the ProAdvisor program and certifications.
Let me show you how:
- Access the QuickBooks Online Accountant sign-up portal.
- Ensure to have the correct Country.
- Click the Sign in dropdown and choose QuickBooks Online Accountant.

- From there, log in with your credentials.

- Choose the QuickBooks Accountant company to use.

- Once logged in, you can find the ProAdvisor tab in the left panel.

Moreover, you can visit this article for detailed information about setting up your QuickBooks Online Accountant: Getting started with QuickBooks Online Accountant.
Additionally, I've added this article as your future reference in case you want to add and organize your clients in QuickBooks Online Accountant: Add clients to QuickBooks Online Accountant.
Let us know if you have other concerns with getting QuickBooks Online certification or other QuickBooks-related issues. We're here to help you in any way we can.