Badger Face ram lambs often stick their heads through the fencing to get to the best looking hawthorn leaf of all. I've known a horn be ripped off completely, which is a fairly bloody business. I wash the area off as best I can, use a plastic wound spray to stop it seeping and put a little Spot On near the base of the horn, to stop maggot eggs hatching.
My ram lamb kept ripping his horns, I had to keep treating in the end I found out how he was doing it, he was sticking his head through fences or small gaps, as he likes to browse more than graze, he is a crossed mountain sheep probably explains why, and then pulling it back. I soon put a stop to this and no damage ever since. He always healed very quickly, but now has one shorter than the other, he is going next week, so should taste nice

The most important thing is to keep it clean and possibly if it is a big horn and it hasn't come out or is very serious mangled it will need a vet. Depends how bad the damage and how confident you're with dealing with it. However reading the original comment it doesn't sound very serious, do keep an eye out though in case they start ripping them. Mine incedentally is a friesland X Pedigree Torddu, so very mischevious