In TurboTax Online, you can clear and start over as long as you haven't paid or registered yet (free users are asked to register their accounts before they file).
Note: You can’t clear and start over using the mobile app. Instead, log in to your TurboTax account from a desktop or mobile browser to clear and start over.
- Sign in to TurboTax Online and open your return by clicking the orange Take me to my return button.
- With your screen maximized, click My Account (at the top of your screen toward the right) and select Clear & Start Over. (If on a tablet or phone, you may find the Clear & Start Over option by clicking the three parallel lines, or “hamburger”, in the top left corner.)
- Answer Yes to Are you sure you want to clear your return?
- After your entries have been cleared out, we'll prompt you to select a TurboTax product so you can start over from the very beginning.
Despite the answer above, you CANNOT delete or start over once you've paid or registered. -- not even on a desktop.
It's very frustrating as they've made a mistake on my state return... my only option is to abandon it and go elsewhere.