There may not be a button. It may be more of a setting. From what i read on that laptop the wireless is automatic, which would mean no button would be needed. But there would be some sort of application on the Thinkpad where you could look up and find available wireless signals, choose one, and connect to it.
On my HP it is controlled by Windows and looks something like this
Mine is green and in the task bar. If you do not see one you may want to check where you view your available networks (may be in control panel or under start menu depending on which Windows you are running)