What they mean is that you gotta treat it like «trying to sleep». You won’t go to sleep faster just by focusing on it. In fact this will make it harder for you to sleep. You have to «fall» asleep by letting go. In the same way to have to «let go» of trying not to stutter, because the more you think about your stutter the more you will stutter. But also you can’t think yourself to trying not to think about stuttering. This is the same as not thinking about a pink elephant.