1. Find where your Crime Boss: Rockay City copy is installed. The location of this folder will vary depending on your installation preferences & storefront.
   Steam
   
   EGS
   
2. Extract the contents into CrimeBoss\Mods.

Unzip NoCampaignWeaponSkins.zip to CrimeBoss\Mods in your game directory, so you have CrimeBoss\Mods\NoCampaignWeaponSkins\Content. (This is not the same location as UE4SS mods.)