Thanks to a direct email from David Squance, I was encouraged to pursue further. A look on the web brought me to this site <https://itstillworks.com/12310138/how-to-convert-an-m3u-to-an-mp3-online-for-free>
The file that I wanted to work on had, actually, been imported to iTunes from the iPhone.
The "itstillworks" page suggested a right-click on the iTunes file in question. That brought up a box which offered, "Show in Finder". By selecting that, I was shown the actual file and could drag that to my audio-editing program, "Amadeus Pro".
I hope that this might be of help, should anyone be in need of such advice.