Leading from the wrong (nondummy) hand in bridge
From the Laws of Contract Bridge - 2014, 

Law 55 - Declarer's Lead Out of Turn


  When declarer leads out of turn from his or dummy's hand:
  A either defender, without consultation, may accept that lead as provided in Law 53; or
  B. either defender, without consultation, may require declarer to retract that lead. Then,
   1. if it was a defender' turn to lead, declarer restores the card led in error to his or dummy's hand without penalty.
   2. if declarer has led from the wrong hand when it was his turn to lead from his or dummy's hand, he withdraws the card led in error and he must lead a card from the correct hand.
  
  If declarer adopts a line of play that could have been based on information obtained through his infraction, the offenders should adjust the score to redress the damage.


So, in direct answer to your question, and assuming no inappropriate information was obtained by declarer through the infraction, once a defender requires declarer to retract the card led in error declarer restores it without penalty and leads (any card of his choice) from the correct hand.

In a club (other than a Duplicate Club) a slightly more formal alternative law may apply using the services of a pre-appointed Arbiter, if such is available. I understand from your description that this is not the case fr your question.