For a detailed tutorial on using this mod to create a custom armor texture, please see the accompanying youtube video.

If you have not already used UXM to unpack and patch your game files, you will need to do so for this mod to work.
https://www.nexusmods.com/sekiro/mods/26

To complete your custom armor, you will need the Yabber mod which can be found here:
https://www.nexusmods.com/sekiro/mods/42

A free photo editing site can be used to create your armor, and this one works well.
https://www.photopea.com/