HOOOOOOOOOOOOOOOW!
Why would you want to? Young kits are perfectly capable of taking a pellet of chow as soon as they are big enough to eat solid food. In 40 + years of raising small breed rabbits, we've never had one that couldn't.
We all try to avoid buying pellets with "fines" in it rather than making them! You could grind them in a blender or a food processor as well as a coffee grinder. You could do them with a rolling pin or mallet as already suggested or you could use a mortar and pestle.
toneman 2 has given god advice but why do you need to crush the pellets as they need to chew they to help wear there teeth down. If it is because you rabbit is off it food and you are try to syringe feed it them you are best get recovery from your vet of better yet as that can be hard to use hippo stage 1 tomato and carrot baby food.
I like the bag trick with a rolling pin. You can also grind them by hand yourself with a mortar and pestle, but that tends to make a mess if your hand slips and knocks it over. Keeping everything in a plastic bag contains it all.
Put them in a sandwich or other storage bag and roll over them with a rolling pin or hit them with a hammer or kitchen meat mallet (the smooth side).
a coffee grinder is fine. you could also use a food processor or spice grinder. ive tried using a hammer but it doesn't work well
