The guide writer uses Maya, so this process may be different if you use Blender or Zbrush. They have also set up their own workspace with each of the gendered models to use as a reference.
If you are going to be making a costume that all genders can use then you’ll most likely need to make three separate edits of your model due to the size and shape difference of each gender.
Be sure to name your models something you can remember and keep track of. My naming convention usually goes like, “GEO_BodyPart_CostumeName_Gender.” So if I was making sunglasses I would name my model, “GEO_Head_SunGlasses_M” for Male and then _F and _H for the next two sunglasses for Female and Huge
Exporting Your Model
This is my experience using Maya and exporting as obj, I do not know if this applies to any other software or export file types. When you’re happy with your model you’ll need to export your costume in a certain position depending on the costume slot you’re using. Each slot uses a different position, some I have catalogued and others I have not yet. Most of the time you can expect it to be close to 0,0,0 or the center of the world.
I have premade models set up in various positions that most accurately tell me where my model would appear once it’s in game. I set up the item on the dummy body part for each gender, then select all the models I want to export, and export under the name of something like, “GEO_BodyPart_CostumeName.obj”