so do I upload the .fit file directly to Garmin Connect to put the .fit file back on my watch and then upload to Garmin Connect? And if I put it back on my watch how do I do that?
You cannot put it back to your device once it's been removed. If you want to manually upload the .fit file you can do that from Garmin Connect
Garmin Connect does not put files on your computer, but when you first loaded them to GC they were stored on your PC with the Ant Agent.
If you have since deleted your old activities from your PC (when creating a new account?) then I suppose they are gone (in the form of a FIT file). After all they were only originally on the watch and sync'd to the PC.
Now as for exporting a file from GC... I have never tried it before today, but it appears the "URL Trick" works for me.