The IRS will start processing returns on Feb 12. Until then TurboTax will hold your pending e-filed return. Pending returns can not be changed. If the return is accepted you will get an email. If the return is rejected the e-mail will tell you what to correct and you can make changes before
e-filing again. Amend to change an accepted return. Instructions below. https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...
You cannot unregister. Once you have submitted payment, deducted the TurboTax fee from your refund, or registered, you cannot erase your return and start from scratch in TurboTax Online.
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Or if it doesn't let you clear and you haven't paid and filed you could just start a new account. Online is only good for 1 return per account. But you can use the same email address for 5 accounts. How to start another return in the Online version