You may have to fool the program that the tax return has been already been filed. In the File section of the program select the option to File by Mail. Go through all the interview screens to complete this section. The software should now recognize that the tax return has been filed so that you can amend the tax return.
To amend a tax return that has been filed when using the TurboTax desktop editions -
Click on Federal Taxes (Personal using Home & Business)
Click on Other Tax Situations
Scroll down to Other Tax Forms
On Amend a Return, click on the start button
