After you file

 

As long as you have not yet actually filed (i.e., not yet efiled or actually mailed the return), you can make changes.

If TurboTax thinks you are finished you have to open your return back up.

·        Log in and go to your 2018 Tax Timeline.

·        If TurboTax thinks you are finished, there will be no "Take me to my return" (continue return) button.

·        So in that case  then  scroll down to Add a State."  (you don't really add one; that's just to get the return to open up.)

·        Once the return is open, you can make whatever changes you need to before filing.As long as you have not yet actually filed (i.e., not yet efiled or actually mailed the return), you can make changes.


NOTE:
  Do NOT use this method to open a return to make changes to an already-filed return (one that has actually been mailed or efiled.)   If you later need to make changes to an already-filed return, you have to go through the formal amending process, and your return must start off exactly as originally filed.