You got your free credit report through the Annual Credit Report site and you found an error. Now what?
This is fairly simple. First, you send a letter to the credit bureau agency with the error (send this certified mail, return receipt requested, so you prove that you sent the letter) and explain the error. From the moment they receive your letter, they have 30 days to either prove the accuracy of the entry or remove it completely.
Then, once the 30 days is up, the credit bureau should contact you with their decision. If they prove the accuracy and you still know it to be wrong, you will need to contact the creditor directly to resolve it.