If you haven't efiled or mailed your return or it rejected you can go back in to finish and change anything you want. Do not click on Amend!
Click on Add a State to let you back into your return.
From Tax Home (the first screen you see after you sign in), scroll down to Your tax returns & documents. You may have to select Show to open the drop down.
Select 2021, and then select Add a State (you're not actually adding a state, this is just the workaround).