Non steam game

I have a bunch of ds roms downloaded but I have to launch them trhough emulation station the games work and everything but I want them to be a non steam game so I can add custom art. Very small problem but I'd like to be able to scroll through my library and see the art for the games im playing. It's not just ds games I also have switch Playstation and more but right now im playing ds games so that's the one im really focused on right now. Any tutorials that im just missing on youtube?