Did you go to the end and hit the big orange Transmit Returns Now button and file it?
DO NOT CHANGE ANYTHING YET! WAIT. If you did change it then put it Back.
You cannot change or add anything on the return that you just e-filed. It is too late, just like when you put an envelope in a US mailbox.
Now you have to wait until the IRS either rejects or accepts your return after Jan 27 when the irs starts processing returns. If your return is Rejected you can go back into your account and fix it, then resubmit it.
But if the IRS Accepts your return you have to wait even longer for the IRS to fully process your return and you get the first Refund. You will still have to pay the tax due if you owe on it. THEN you can prepare an amended tax return and mail it in.
How to amend
If you have not filed the 2020 tax return just go back to the section of the program to make your correction.
If you have filed the 2020 tax return then it cannot be changed, retrieved or cancelled. You will have to wait for the IRS to either accept or reject the tax return. If rejected you can make your changes and e-file again. If accepted you will need to wait for the IRS to process the return and issue the tax refund.
Then you will have to amend the tax return that was filed using Form 1040X. The amended tax return will have to be printed, signed, dated and mailed by you to the IRS. The IRS will take 4 months or longer to process the amended tax return.
The IRS will not be accepting or rejecting any 2020 federal tax returns until late January 2021.