If you have not e-filed or mailed the 2019 tax return then you can make changes to the 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.