By it peeling away. I’m guessing it’s not clear coated over it. You can try burnishing some scotch tape with your finger over what’s left. It may lift the rest off when you peel off the tape. If that doesn’t work you could put some solvaset on it to soften it up and it should lift off with a q tip without harming the paint. Both methods are relying on the fact that the decal was never sealed.