To adjust the brightness in the dashboard, first select the charging station for which you want to change the brightness. Then go the 'Charging station configuration' card, press the pencil next to 'LED brightness' to edit the value.
To adjust the brightness in the app, go to 'Control' and press 'Smart devices', select the charging station for which you want to adjust the brightness, then you adjust the value of the LED with the slider.
Note that changing this setting will have effect on the white and colored (red/green/blue) light.