Hi there, slgreer2.
You're correct, you can't delete the Extra tax withholding section or Additional income tax amount you want deducted from each paycheque in QuickBooks. However, you can update it by entering zero in the field. This ensures the extra withholding won't be applied during payroll processing.
Please note that you can't leave the field blank, as QuickBooks will show an error message. Ensure to enter zero in the field to properly save the changes, as you can see the screenshoot below.

As always, you can leave a comment below for additional questions or concerns.