Don't know if you have already found out how to do it but there should be 3 types of custom model in that mod folder.
1. Accessory models or just a singular accessory. To install, extract everything inside to sexmod => custom_models => singleplayer then you should be able to customize the specified girl with the girl wand.
2. The second type comes with only a single "assets" folder. EXTRACT it then open the mod with 7zip or WinRar and put the "assets" folder in there, go into the game and spawn the girl that the mod applies to.
3. Resource pack models. Most of them have been extracted so simply put them in the "resourcepacks" folder, if done correctly they should show up as resource packs in-game like this.
View attachment 3005176
I apologize if my explaination is a bit confusing in some parts, english isn't my native language.