Advanced payroll: an employee was given portal access with the wrong email. When the correct email was added, the wrong one remained. How can it be removed?

Welcome to the Community, @Oliver.

If you're referring to an employee added as a user to your QuickBooks account, I recommend deleting the wrong one from the Payroll Settings section.

Here's how:

1. Click the Gear icon in the upper-right corner.
2. Select Payroll Settings.
3. Choose Manage Users.
4. Click on the bin icon located on the right hand side of the user's name. 
5. In the confirmation popup box, press OK.

For future reference, check out the Manage users in QuickBooks Online Advanced Payroll article. It provides an overview on how to delete an existing user.

If there’s anything else I can help you find in QBO, post a comment below. I’m here ready to assist further. Have a good one.