how do you access the driver side front signal bulb on the '04 s40? i can't get to it from inside the engine compartment

 

Have you checked the owners manual? There is one online.
Volvo Cars | Community | Your Volvo

 

The turn signal housing is held to the headlight housing via a phillips head screw. You can see it looking straight down from the top/back of the headlight housing.

Loosen the phillips head screw on the back side of the headlight housing. Pull straight forward on the turn signal housing. Do not pull up/down or left/right. It comes straight out same as the headlights shine. It's not difficult once you see it.