This is achieved by inserting the screwdriver *at an angle* thus: It takes a little practice, but with a little care it can be done quickly. Once the assembly has been released, twist the bulb holder to remove it from the lens assembly and replace the bulb. Put it all back together and clip back in place.
Easily replace a wing / door mirror on a Ford Focus 2004 - 2010 (European version). This video also shows you how to just change just the mirror glass on the
Carefully unclip the heater controls (3 clips) and pull the fascia forward to access the wires behind. Unplug whatever you feel is necessary to easily access the lighter socket and lighting ring. The back of the socket will have a twin connector as in the photo below, the illuminated ring will be one wire (not shown) HDdpsrb.