Are you referring to the Activation Lock? You do not need your serial number to unlock your iPhone or remove the Activation Lock. What you need is the Apple ID and Password that was used to put on the Activation Lock.
I understand that you are referring to the passcode that is used to get to the Home Screen of your iPhone. I also understand that your iPhone has been disabled. You will have to reset the passcode to your iPhone by following the instructions in this guide published by Apple 👉 If you forgot the passcode or if your iPhone has been disabled. You will need a computer to execute this procedure and all the data on your iPhone will be erased.
Axel F.