You message indicates you are using the TurboTax desktop CD/Download edition of Home & Business.
When you start the program and want to amend your current tax year return, on the opening screen Continue Your 2018 Tax Return click on the Amend a Filed Return button.
Or -
Continue your 2018 tax return.
Click on Federal Taxes (Personal using Home & Business)
Click on Other Tax Situations
Scroll down to Other Tax Forms and click the start button on Amend a Return
