I want learn to Change or Reskin FBX file using Blender in Unity3D

Hi, I want learn to: - Reskin FBX file on Unity3D project using Blender (I know using Blender, want only the method to import and then export the result + integrate it to the game again). - Change character in the game and replace it using the same BONES (I want to learn how to adapat the existing BONES to a new character). - I want integrate new object in an existing environement + collider. I want do this for an existing game (SubWay Runner) using Team Viewer or Video if you have, just quick steps. My FBX files are not compatible with Blender, so you need to show me how to convert them to a right version. I will pay fixed price for this project: 20$ Thank you.