To disable auto-brightness on your laptop’s external monitor, the following steps should be followed:

1. Locate the brightness adjustment setting on your laptop: Choose the brightness settings from the system tray or from the controller of the external monitor.
2. Check the auto-brightness option: Look for the auto-brightness setting and make sure it is turned off.
3. Adjust the brightness manually: Manually adjust your monitor's brightness and contrast settings according to your preference.
4. Save the settings: Save the changes and close the window.