If the mower is starting and running, the engine might not be badly damaged.
Drain the gas from the tank into a clean container and dispose of properly. Tilt the mower on the side with the carburetor up and remove the blade and blade adapter.
Look at the underside of the deck for any damage there.
Set the mower up and put a small amount of gas in the tank. Start the engine without the blade for a few seconds. Don't run the engine long as it might damage itself without the weight of the blade. If the noise goes away with the blade removed, you can probably replace the parts that were damaged and the mower will be ok.
You can order the parts you need at
If you have more questions, reply on this thread and I will be glad to help.