If you have NOT filed the 2020 tax return -
If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over with a lower priced edition. Click on Tax Tools on the left side of the program screen while working on the 2019 online tax return. Click on Clear & Start Over.
What do you mean reverse? You mean revise? What years?
Did you already file 2020? You cannot cancel or change or add anything on the return that you 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. Which won't be until Feb 12 this year. If your return is rejected, you will be able to go into your account and add or change it and resend it. Click on Add a State to let you back into your return..
If the IRS accepts your return, then you have to wait until it has been fully processed and you have received your refund or paid the tax due. THEN you can prepare an amended tax return 1040X and mail it in. You cannot e-file an amended return. Meanwhile, DO NOT change anything on your return until you start the amended return. If you did change or add the missing info then take it out and put your return back to the way it was when you first filed it.
You can check your efiling status here,
How to amend an Online return