If I just found out that my first husband is not dead after being told that he was so I remarried 11 years ago, what do I need to do?

In theory, you have committed bigamy.  However, there is a defense called the Enoch Arden defense.  An excellent summary of this can be found at the following link.  http://legal-dictionary.thefreedictionary.com/Enoch+Arden+Doctrine  This defense protects you from criminal charges for the new marriage.  You should file a divorce action.  This will make it clear tht husband #1 is no longer married to you.  When the divorce from husband #1 becomes final, your marriage to husband # 2 should be valid.