You need to add an amount to line 30 for the Recovery Rebate Credit? Or enter the 3rd Stimulus payment that you received last year? Line 30 is only if you didn't get the full amount or qualify for more.
To change a return If you haven't mailed or efiled yet, see
https://ttlc.intuit.com/community/tax-topics/help/i-want-to-change-a-return-i-ve-printed-but-haven-t...
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).
Why are you mailing? Why can't you efile? When you are ready to file you can try to switch to efile.
https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online...
