How do I use a .tax file to amend a 2017 return? Context: I want to amend my 2017 tax return. I've downloaded the .tax file

When I open the app, I have the option to amend a return or open a .tax file. Doing the former wants me to put in all the information again. Doing the latter just shows the tax return I've already filed. I want to use the existing .tax file to start the amendment process.