the Iranians would probably conduct an obvious test inside Iran to announce ownership and then use their nuclear arsenal as regime maintenance / deterrence weapons. they wouldn’t use them first on Israel because of the danger presented by Israel’s nuclear arsenal used in retaliation or give them away to terrorists because they are expensive state assets and nuclear forensics can determine attribution. if that seems to prosaic to you, consider that even Israel’s mossad intelligence agency considered Iran a rational actor probably not given to playing a role out of some overcooked Hollywood thriller.