When you amend your tax return to remove the erroneously entered IRA contribution, TurboTax will simply delete the Form 5329 that originally reported an excess contribution. You'll need to prepare a corrected Form 5329 outside of TurboTax, and possibly a corrected Form 8606 as well, to show zeros where it previously showed the IRA contributions and mail them along with the Form 1040-X that TurboTax prepares.
