Soften it up with some olive oil or a warm wet cloth before you begin it will make the process smoother. These occur on people, dogs, chickens pretty much anything with oil glands. If you need guidance there are lots of videos on removal. Good luck.
I also notice this was two years ago! But...my chicken has something like this in her back that seems rock hard. She is also limping greatly about the same time I noticed it! any advice?