You need to save the original tax return before amending. Then save amended return with a unique name.
In the File menu on the top left of the desktop program screen click on Save As... to give the return a unique name.
See this TurboTax support FAQ for how to cancel an amended return when using the TurboTax desktop editions - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/cancel-undo-amended-return-tu...
