when I use the editor it auto detects the save directory (probably by reading registry).
you then click the save you want to use and hit load.
But be warned it seems a bit buggy, on some of my saved games it doesnt even detect who is in the party correctly and my chocobos wrong, like detecting black chocobos as standard so I expect if I made it save over my previous save it would mess up my game. I did use it to give aerith the umbrella in an early save fine tho, since that item is impossible to get.
