When you filed your tax return, did you click on Transmit to e-file? Did you download and save a copy of your completed tax return? If so, does it show the EIC on any of the downloaded forms? If you have already filed your return, you won't be able to make any changes until your return has been accepted or rejected by the IRS. If rejected, you would need to correct any information that caused your return to be rejected as well as make any other changes to your return that you see fit, then proceed to resubmit your return. If accepted, you would need to amend your return. You can follow the instructions in this FAQ here to amend your 2020 tax return.