bb? More like a slug
Well to fix it properly, you would need to grind the area down to remove the rust/paint, including in the hole. From there you could cut a square around the hole and weld in a new patch of smooth metal.
Or you could go the easy route ans just fill the hole in with filler but it looks pretty big/deep to try that. Also rust is more likely to return and will really look bad showing up in the middle of the door on a white car.