Ramban on Exodus 11:10/רמב"ן על שמות י״א:י׳

1AND MOSES AND AARON DID ALL THESE WONDERS. These are the wonders mentioned above. Scripture states this now because it completes [the narrative of] all the deeds they did [before Pharaoh], including the decree of the plague of the firstborn of which they already informed Pharaoh, for in the actual slaying of the firstborn, Moses and Aaron had no part.