Well, first of all you should probably ask your local garage first and if they cant call the dealership. GL
If only the low-beam is out, you will need to replace the low-beam bulb. It is probably not necessary to replace the entire headlight assembly.
how to replace 2007 Mercedes GL450 Headlight Bulb Low Beam
To change the low beam lights on a 1991 Acura Integra open the hood and prop it open. Find the headlight housing and locate the smaller bulbs. Pull those off and replace them.
To replace the low beam headlight bulb on the driver's side of a 2009 GMC Sierra 2500 HD Diesel, first, open the hood and locate the headlight assembly. Disconnect the wiring harness from the back of the headlight by squeezing the release tab, then remove the rubber dust cover. Twist the bulb socket counterclockwise to remove it, replace the old bulb with a new one without touching the glass, and reassemble by reversing the steps. Ensure everything is securely connected before closing the hood.
A sealed beam headlight is just that. The unit is sealed and you replace the entire light. A composite is made of pieces that's why the name. To replace a composite you put a new blub in the back.
Carry it to dealer who will replace on low beam headlight for $15 +/- dollars in about 5 minutes.
The headlight has two filaments. One for the high beam and one for the low beam. The most likely reason the high beam is out is because the high beam filament is broken. Replace the bulb and it should fix it.
replace the high beam bulb
The Low Beam AND High Beam are in the same bulb. The procedure to change it will be in the owners manual.
replace passenger side low beam headlight
replace the low beam headlight bulb
you will probably have to replace the headlight switch.