You didn't say whether you are using TurboTax Online or the C/D Download TurboTax software. If you are using the CD/Download software you should have kept an unmodified copy of the original filed return, and saved another copy with a different file name to amend. Then you can get back to the original by opening the saved original file.
TurboTax Online saves only one copy of your tax return. Once you make changes, such as by amending it, there is no way to get back to the original. There is no backout or undo.
When you start an amended return it resets the Refund/Tax Due to zero. That's how an amended return works. It will then show the additional refund or tax due caused by the changes in the amended return. Since your amendment is not changing your tax, it will remain zero.
I don't know what you mean by "Restart." There is no Restart option in TurboTax.
