Flight deck access system

Please explain what the “flight deck access system controller” is, and describe its function.......
  
     
 

The main purpose of the flight deck access system is preventing unauthorized entry into the cockpit.

The flight crews can lock/unlock the door with a switch (usually on the overhead panel).

There is a panel on the outside of the door that a numeric pass code that can be punched in to allow the door to unlock.

What can be done if the numeric pass code has been forgotten?

I have no clue as to the type of system installed on your aircraft.

This would be a add-on from the the original delivery configuration, so I would think you would find information in a Supplemental Maintenance Manual.