After you file

If you used the TurboTax online editions to amend the 2018 tax return, then you will need to return to the 2018 online account to make changes to the amended return.

When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state.  

This will take you back to the 2018 online tax return where you can make changes to the amended return.