It's not as simple as that...
You have to load your character file. I recommend the .pac file. Not the FitChar.pac (because newcomers tend get confused about this way too easily), the FitChar0#.pac (ex: FitMario02.pac).
Then just save as a .pcs
But for the other way around...Loading the .pcs and saving as a .pac will most likely, if not always freeze/crash the game.
But if your model only comes with a .pcs, export the model and textures. Then open up an unmodified FitChar0#.pac, replace the model and textures, and save as a .pac
I do appreciate that you made a tutorial for a common problem, but your current tutorial won't really work.
i made this for the people who download hacks that only have a .pac or .pcs...
this has always worked for me.