Once a tax return has been e-filed it cannot be canceled, retrieved or changed.
If you have e-filed your tax return and need to change, add or delete information on the tax return then you will need to wait for the tax return to either be accepted or rejected by the IRS.
If the tax return is rejected then you can make your changes and re-file the tax return.
If the tax return is accepted then you will have to amend the tax return to make your changes. An amended tax, Form 1040X, return can only be printed, signed, dated and mailed by you to the IRS, it cannot be e-filed. The IRS will take up to 4 months to process the amended tax return. Wait until you have received the tax refund or the taxes owed have been paid and processed by the IRS before amending the tax return.
On the Tax Home web page when the the Form 1040X for amending a 2019 tax return becomes available there will be a link - Amend (change) return
I didn't E-file but printed out the papers to check and now I can't fix what is wrong!
@vtgrammie As long as you haven't already mailed your 2020 paper return, you can switch to the e-filing method. This will allow you to get back into your tax return and make adjustments as you see fit. See the instructions in this link here to do so.