How do I start over on my tax return

You can erase your return and start from scratch as long as you haven't submitted payment or registered.

1. Sign out of the mobile app (under App Settings).
2. In your web browser, use your app login to sign in at TurboTax.com and select the Take me to my return button.
3. On the welcome back screen, in the left-side menu, select Tax Tools, and then select Clear & Start Over (click or tap the 3 lines in the upper-left corner if you don't see this menu).
4. Answer Yes in the pop-up to confirm.
5. Select Sign out at the very bottom of the left-side menu.
6. Now sign back in to the mobile app, and you'll start with a clean slate

https://ttlc.intuit.com/questions/3177005-how-do-i-clear-and-start-over-in-the-mobile-app

I don't have a mobile app. Do I need to sign on to turbotax.com in order to start over with the downloaded application on my laptop?  I haven't filed anything yet.

No.  If you have the Desktop program installed on your computer to start over you need to start a new return.  Go up to FILE - NEW

Thanks. Will I run into problems with importing from the same 2019 tax file a second time? 

No.  Each return is separate.  Save the new return with a different name than the first one you did so they don't get mixed up.  Or delete the first one.  Each return is saved in a separate data file ending in .tax2020 and should be in your Documents in a Turbo Tax folder.

What if you have submitted payment and discover mistakes on the printed return which I have to mail anyway? I have to pay again?

You can file an amendment after your submitted return has been processed by the IRS. See our FAQ on How to amend a return. In addition, TurboTax allows you to amend your return for no additional cost to you.

@collinsb032