If it isn't that big of a clump I wouldn't worry about it too much as eventually the fur will shed and the clump will come out so that you can easily just pull on it and it will come off. If it's a larger size I recommend trying to work on it with a flea comb or else taking some nonscented baby wipes and working it out.
If it's small it won't really hurt the chin and they may groom it out themselves.