CITROEN DS5 Owner's Handbook Manual page 62

Locking the front and rear
passenger doors
Open the doors.
On the rear doors, check that the child lock
is not on (see Child Safety).
Remove the black cap, located on the edge
of the door, using the key.
Insert the key in the socket without forcing
it, then without turning it, move the latch
sideways towards the inside of the door.
Remove the key and refit the cap.
Close the doors and check that the vehicle
has locked correctly from the outside.
Unlocking the front and rear
passenger doors
Pull the interior door opening control.