How do I add my exisiting intuit payroll account to my quickbooks online account?

Good day, robin39.

QuickBooks Online and Intuit Online Payroll are different platforms. Therefore, adding the existing payroll account to your accounting program is unavailable.

What you can do is export your payroll data to QuickBooks Online. You will need to set up the export preferences to do this. 

Here's how:

1. Log in to your Intuit Online Payroll account.
2. Go to Setup, and under Export, click the Preferences link.
3. Choose QuickBooks Online from the Your Accounting Software drop-down list.
4. We will search for any existing QuickBooks Online accounts under the current user ID. If we can't find an account, you will be prompted to log in to your Intuit Account.
5. You may be prompted to select a security question and answer
6. If an account is found, you can continue to the export process.
7. Complete the connection process.

I've got an article for more details on the steps above: Setup export of IOP data to QuickBooks Online (QBO).

You can always get back to me if you need anything else. Thank you.