You’ll need some kind of editing software, Photoshop is the recommended.
If you do not have this download this: https://www.dropbox.com/s/7s23ngkc94gofh4/setup.exe?dl=0
You will require a licence key through the setup with is: 8MEH-RU7JQ-ACDRM-MQEPR-G3S23-FEMBR-ACED
Another editing software, Suggested by @Such_Meme_Many_Skill is: https://www.dotpdn.com/downloads/pdn.html
You need VTF Edit, You can get this from the internet (As most things) but here’s a link: https://developer.valvesoftware.com/wiki/VTFEdit (Carful of the fake download ads)
Once you have downloaded this search through this DropBox for the guy you want: https://www.dropbox.com/sh/28p9p5xkm70nya9/AACRUg_ZOBsVMl7Qele6XTYUa?dl=0 There is a v_model and a w_model , you need both.
They should look like this: (Obviously for you gun)
Save these in your documents and then open VTF edit then open the previously saved file.
The weapon “net” will appear, copy this and paste this into a word document and you can save as from there, you can not directly do this from VTF (Idk why)
Creating and adding your skin:
To make you skin it is as easy as opening the weapon “nets” into Photoshop and editing the accordingly, look art pictures of the full gun online to work out what’s what on the “nets”.
Once you have created this and saved it as a .jpg or a .png you can then test them in game.
Use the following tutorial to show you how (Bit outdated): https://www.youtube.com/watch?v=C22L4ZLLfBY
Creds to @Doppel for this!