Sign onto the TurboTax website with the userID you used to create the online account - https://myturbotax.intuit.com/

If you do not land on the screen that  shows Take me to my return, then follow this procedure - 

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 to complete and file the tax return.