Yes, you can delete the data you have entered with our clear and start over feature in TurboTax but you won't be able to use this if you've already registered, submitted payment or deducted the TurboTax fee from your refund. Please see this TurboTax FAQ for more information: https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-online/00/26444
If you already filed your tax return you won't be able to do this. If you missed adding a W2 when filing your tax return or other information. First, you'll want to determine if the IRS or state has accepted your tax return. You can check your refund status here. If they have accepted your return, then you may need to amend your tax return. If your return was rejected, you can correct the reason for rejection and your return and resubmit. You will receive an email from us on how to fix the return.