Yes, you can soak its little rear until it loosens or you can moisten it with a warm wet rag. Some people I know just pull it off, butt fluff and all. Ouch! Anyway, this is pasty butt and can cause serious blockage issues so you'll want to clean it off as soon as you see it.
My experience is limited but most of the pasty butt I've seen I believe was caused by my brooder being too warm. Some chicks just get pasty more easily (more fluff) so you can apply olive oil and it will have a harder time sticking.