During an emergency solely related to aviation (ie not a medical situation), suppose that some airline passenger believes that he/she can help in the cockpit. Since the cockpit door is locked for security, how can he/she volunteer their services and enter the cockpit to try to help? I am guessing that someone with minimal flying experience (such as an amateur gamer of Microsoft Flight Simulator) can help.
This question presumes the ability of airline passengers to help. Here is a real-life example: According to the Mayday episode on Air France Flight 447, while attempting to recover from a stall, the first officer pushed his yoke up (wrongly), while the reserve first officer pushed his yoke down (correctly). This opposition in pushing nullified each other and the plane continued its fall in its stall.
The captain was out of the cockpit at the start of the stall. He returned afterwards (I don't recall exactly when), spent some critical time surveying the control panel, but didn't apprehend the problem in time. Might a passenger have helped to perceive the problem (without spending time examining the instruments)?
Please feel free to edit this post; I'm not an expert on aviation.