TurboTax online accounts cannot be deleted.
You can clear all data from the tax return and then close the TurboTax window on your browser.
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. Click on Switch Products on the lower left side of the program screen while working on the 2025 online tax return. Click on Clear & Start Over