|You can probably adjust the brightness on the monitor itself, and you may be able to adjust the brightness in the Display settings in Windows too.|
Your monitor probably has buttons that can pop up an OSD (On Screen Display) and in those settings you can adjust the brightness. See the manual for the monitor if you need to.
RIGHT click on a blank area of your desktop screen - choose Personalize - Display Settings - Advanced Settings. Sometimes you can adjust the brightness there too somewhere.