TurboTax online accounts cannot be deleted.
If you have not filed a tax return you can clear the tax return and then just abandon the account.
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 Tax Tools on the left side of the program screen while working on the 2021 online tax return. Click on Clear & Start Over.
If you want to cancel the Advantage subscription see the procedure in this TurboTax support FAQ - https://ttlc.intuit.com/community/downgrading/help/how-do-i-cancel-my-turbotax-advantage-subscriptio...
I would like to cancel my subscription and not have TurboTax software sent or billed.
See this TurboTax support FAQ for how to cancel your TurboTax Advantage subscription - https://ttlc.intuit.com/turbotax-support/en-us/help-article/change-service-level/cancel-turbotax-adv...