The desktop program by design is never connected to the online system ... some people prefer that security. When you use the downloaded version it is your responsibility to safeguard the information. I always suggest saving the files on more than one thumb drive along with the PDF of the returns.
If you used the 2018 online program to complete the original return you can download the .taxfile again and complete the amended return that way. If not then all you can do is recreate the original return.
