Welcome!!
It's the beam angle setting. I'm not sure where the adjuster is on a 500L, but essentially it lowers the headlight beams based on the vehicle load. The numbers basically relate to how many passengers are in the rear of the vehicle as this will affect how low the rear end is, and therefore make the headlight beams point further upwards.
The adjuster is usually somewhere near the steering wheel. Park on a flat surface with the headlights pointed at a wall, move the setting from 0 to 1 to 2 to 3 and you'll see the lights raise and lower. If it's just going to be the driver and front seat passenger, set it to 0 and all will be well.