To start the dimming process, quickly switch OFF and ON the light fixture from the wall or power switch. After flicking the switch the dimming process will start.
It is always possible to change the default brightness by starting the dimming process again.
To set the default brightness level back to maximum, just flick the power or wall switch OFF and ON once and the dimming process will start again. When the brightness level reaches the maximum value it is set as a new default for the light fixture.