Can someone help with amending a 2017 return which I filed in 2019? It has been less than 3 yrs since I filed it. That's ok with IRS to do.

So I downloaded my 2017 .tax file from Turbo Tax online to my computer. Opened my desktop version to amend it, but can't unzip it? The desktop version says it can't open a .tax file older than 2018! What's up with that?