A short video showing a fast and simple method to repair a small area of knock down ceiling. The tools needed are a texturing sponge, an acrylic knock-down blade, and some joint compound or span-lite mud (it's really just a lighter-weight version of a joint compound).
Ceilings in my neck of the woods are never painted and are just sprayed on so doing a repair like this doesn't even require painting. Your ceiling may vary but the principle in how the repair is done is all the same.