I hit a rock and my three hole blade came off. I don't see any screws.. just the blade.. I am purchasing a new blade but I don't know how to attach it back together.

Hi,
Sounds as if you may have broken the bolt in the center and the remainder is still in the crank. Liable to have one of two diamond shaped plates that fit push the blade against the adapter; one bows and holds the outer blade holes on pins cast into the adapter(replace diamond washer and adapter) or one with tabs that go through the holes in the blade and adapter( replace diamond washer with tabs.)
Peace,
Clarke