We sell a lot of assemblies because they are nearly impossible to get apart
after they have aged for seven years.  Probably the best way it to remove
the whole assembly from the car.  The upper fasteners are easy but you have
to drop the face bar to get to the lower bolts. Once the assembly is off the
car you can carefully pry the lens from the housing,  you'll see
interlocking tabs but you will have to reseal the lens when you re-assemble.

A safer method is to put the whole unit (less the bulb) in an oven at 150°
until the moisture has gassed off and not worry about the dust that has
collected inside.  Make sure the weep hole at the bottom is open,  spread
silicone around the joints and be sure the gasket for the lamp seals well.

Good luck,
Bill

Just loosen the bulb and park the car facing south. The sunshine will remove
the condensation in a few hours.