Minecraft-3ds-Image-Flip is a tool that's main purpose is to take a Minecraft skin (PNG), flip it and convert it into a 3DST for Minecraft: New Nintendo 3DS Edition.
Installation
Download the tool from https://github.com/Cracko298/Minecraft-3ds-Image-Flip/releases, and launch it with Powershell: https://github.com/Cracko298/Minecraft-3ds-Image-Flip#usage