How do the door mirrors fold on a Citroen Picasso 2.0 HDi?

If your car is fitted with this feature ('Exclusive' models), then you rotate the mirror adjustment dial to the down position. Turning the dial back up will unfold them.

Do not attempt this if you do not have the Exclusive version, or if your mirror adjustment panel does not have a white triangle in the 'down' position. Forcing the dial to turn down can break the connections inside, and you will have to replace the adjuster.