Completed on line form but never mailed. how do I amend that form?

[Texas Roger]

You don't amend it because you have never filed it. The amended return form 1040X is for persons who have already filed a return and it has been accepted.

Just open your account and go in to make any necessary changes in your tax return. 

[DoninGA]

You do Not amend a tax return that was never e-filed or printed and mailed.  You make your corrections on the original tax return before it is filed.

To access your current or prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/

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 2019 online tax return to make your changes.