Instructions on the download page say:
You will need Wing Commander 1 original files DOS or the Kilrathi Sega. Go to GOG to purchase the game if you don't own it.
Then after downloading Wing Com Reloaded and starting it, you can just point it at the UNZIPPED Kilrathi Sega folder during initial setup. It will also work with the Dos version but sound will be better with KS.