How to Unlock iPhone 6+
This Apple page presents the steps to regain access to an iPhone that is otherwise out of reach because of an unknown passcode. You'll almost certainly lose whatever data is now stored on the phone.

Basically, you'll have to erase the phone using iTunes or Recovery Mode. If you didn't make (or have access to) a backup, all the phone's settings and data will be lost. 

If neither works, you can contact Apple and obtain assistance. You'll undoubtedly have to demonstrate that you or your firm is the original owner of the device.

Good luck!