You cannot delete your account. You can contact TurboTax Support to see about getting your account deactivated.
https://support.turbotax.intuit.com/contact/
You can also clear all your information from your account, using the Clear & Start over option.
How do I clear and start over in TurboTax Online?
As long as you haven't submitted payment, deducted the TurboTax fee from your refund, or registered, you can erase your return and start from scratch in TurboTax Online.
- Sign in and select a topic to continue your return.
- On the next screen, from the left-side menu, select Tax Tools, and then Clear & Start Over (select the menu icon in the upper-left corner if you don't see this menu).
- Answer Yes in the pop-up to confirm.
