(sigh)
You won't get a "confirmation"...
1. Iran would never openly admit that "yes, our forces fired that missile from Lebanon." That would be an ACT OF WAR and give the Israelis what they need to hit Iran.
2. It's not as if there are reporters with Hezbollah/Iran Rev. Guards reporting on what they do. Any reporter who tried would be killed on the spot.
All you can do is rely on intelligence. Apparently the presence of Iranian Revolutionary Guards in Lebanon has been an open secret for quite a long time, and it's also known where the missile came from (Iran). Either the Iranians told Hezbollah how to operate the missile and watched them flip the switch, or it was the Iranian's finger on the switch instead. It matters little. Either way, Iranians had to be on-site to teach the missile's operation at the very least, if not operate it themselves. Apparently Israeli intelligence thinks the latter is more likely.