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.