Users control Apple displays through physical controls as well as software controls that are installed automatically as part of the operating system. These controls often provide different ways of adjusting the same thing, such as brightness.
To access the physical controls, simply check the front or side panels of the display itself, or consult the display's user's manual if you can't locate them by sight.
Different Apple displays have different control configurations. To learn about the controls for the specific display you are servicing, check the service manual for that display or consult the Knowledge ...