To fix a broken driver-side mirror, replace the lens inside of the mirror housing to avoid removing the entire door panel. To do so, wear protective gloves and use a flat implement to push the right side of the broken lens to the inside of the mirror housing, allowing the left side of the lens to stick out of the housing. Carefully pull the lens outward until it detaches from the motor of the mirror.
Some lenses are attached to the motor by four metal brackets around the outside of the mirror, while others are bolted to a metal strip behind the lens. Pulling on the lens forces the brackets or strip to be released from the motor inside of the mirror housing. Dispose of both the lens and the attachment as the new lens has a new set of brackets or a new strip provided.
Secure the brackets or strip of the new mirror lens to the mirror motor. Center the four brackets onto the face of the motor so that the mirror moves correctly when adjusted. For a metal strip, insert the tip of it into a slot located on the face of the mirror. Carefully apply pressure to the mirror lens as you secure it inside the housing. Stop when it is flush to the outer edge of the mirror housing.