Hi there and welcome
Can you tell me please the exact message you see on the screen of the phone?
You will have to reset the iPhone, there is no other way to remove this.
this will remove all your data from the phone and return it to new, but you cannot avoid this, it is the whole reason for the passcode.
To do the reset
Connect the phone to the computer and open itunes
Hold the power and home button down until you see
"iTunes has detected an iPhone in recovery mode..."
Click Restore Phone, let this complete and it should now work
I can also do these steps for you, and have made a request via Additional Services. This is optional, and if you choose to do this, I can, with your permission, remote into your computer while you watch and do all these steps (and deal with any problems that arise during them) for you. Or if you do not choose to take this service, we can continue here. This is no problem at all. Just let me know please.
Else Let me know the results please