Yes, clean is as best you can and very carefully. Search Pasty Butt in the search function and you'll find all kinds of advice. The poo can really cement on there, and you don't want to rub the skin or pull any down out around it's vent. I've read of people running their bottoms under a trickle of warm water, or using a warm, wet washcloth to loosen/soften the poo. Make sure you dry your chick off (people use hair dryers on low and other methods) because you don't want it to get cold.
Once clean, you can dab a tiny amount of veg or olive oil on it's vent to help keep the poo from sticking. And try adding a little apple cider vinegar to the chick water as a preventative measure.
Pasty butt can be tricky - definitely search on this forum and read more advice.