Shoulders are a privilege. If you don't trust the bird, then don't allow him to get on to your shoulder. I rarely allow my bird on my shoulder. Usually it only happens when I am walking by her cage and she jumps on, but she doesn't bite my neck. I remove her immediately. My husband love to have her on his shoulder, so he allow it.
*Sigh.* Since he's refusing to step up for you and is drawing blood:
grab a towel, wrap him up and put him in his cage.
Now your trust will be back to 0%, or near enough. Lesson in this is to not let your bird on your shoulder until you trust them to step up and not bite.
Now you'll have to work on gaining trust, offering treats, chattering, teaching step up, step down.