Unfortunately, you cannot delete or close your TurboTax account. However, you can delete all returns from the account.
When you log in to your account, click on the trash can icon next to a return to delete it.
If you only have one return, it won’t show the trash can. Click on the “Continue” button after “Start a new 2021 return” to create a blank return. Then select “Return Manager” from the “Tools” menu on the top right. Now you should be able to delete your return, leaving only the empty return in the account.
Thank You for choosing TurboTax.