Trying to find reset password (iPhone 5s)

I went to Verizon today to update my iPhone 5s to an iPhone 6 plus. After the transaction occurred they went to reset my old iPhone for trade in and it asked for a reset password. I used my regular 4 digit unlock code and it was incorrect. They told me it had to be a separate unlock code that I setup when I got the phone. I tried everything I could think of, nothing worked. They told me to go home and go to the laptop where I backed the iPhone up to iTunes and I can pull it up in there. Well they kept the phone and I have no idea how to get the code off iTunes without the phone. Any insight? Thank you.