You can't transfer H1B's PERIOD. Your new employer can apply for a new H1B for you. There's no such thing as an "unused" H1B. If you don't go to work for the sponsoring employer (or you quit his employ after you do), the visa is invalidated. Given three years have passed, I suspect you'd be starting over with a new employer. Had you been currently on an H1B, you would have been able to skip a few steps (notably cap issues).