Garmin Basecamp (free download) will do this for you. Attach the Edge, select the relevant Track, then "Export selection" - it should export a .gpx file which you can use to send in for validation.
Alternatively, "TCX Converter" has always worked well for me. See
hereFree download but welcomes a voluntary contribution towards keeping the product fresh.
I believe there are several other things which will do the job; others will be along in a minute to advise, no doubt.
EDIT - P.S. I can't answer your questions about doing it in the Edge with confidence. I have a 705 but I've never explored beyond using the above mentioned methods.