Put em out of business. Bomb their oil refineries. Sanction the bastards.
Better yet, send the computers that operate their refineries a virus that blows them up remotely.
The problem is that Iran can not refine enough of their own oil to supply their own economy. They have to import gasoline and diesel.
They export 90% of their oil from Kharg island in the Persian Gulf. Blow that up and their foreign currency stops.
However, if we do that, they probably activate every sleeper cell in the west. Then attack us everywhere.
So, what is best way to lower their foreign currency sales?
The sanctions that Trump imposed plus you produce so much oil in the USA that we drop the Brent Sea Crude price to $45/barrel.
We bomb their oil refineries—they will bomb ours. They do not need B-1s or tomahawks. They will just use people smuggled in with bombs or torches—They will call themselves with another name but Iran will foot the bill. We have armies of agents in our land.