It is normal for your refund to drop to zero when you select to amend as it begins to calculate the difference between the original return and the amended information it believes you are about to enter.
If you have filed the return, your refund amount has not been affected as amended returns have to be printed and mailed to the IRS for changes to take effect. If you have not yet filed the return but generated and amendment, your refund amount will be restored once we undo the amendment.
To undo an amendment in TurboTax online,
https://ttlc.intuit.com/replies/4170678
If you are using TurboTax desktop software, you can:
https://ttlc.intuit.com/replies/4170766