The Iran deal has NOT been approved by Congress. The House voted against it and the Senate hasn’t voted because Obama never turned over the side deals.
The Senate does not get to approve the Iran deal, thanks to the Corker amendment. The Senate only get to disapprove the deal, then when O vetoes the disapproval the Senate must override the veto to kill the deal. Basically Corker approve the Iran deal with lots of face saving denials for Senators like Cruz bill into the deal. Just like TPA did for TPP.