Hi,
Common failure on these locks is the exterior lock barrel becoming detached from the spindle which operates the internal part of the lock. The spindle is attached by a small roll pin which drops out.
To remove the lock barrel pull aside the door rubber seal level with the lock, you will see a hole which gives access to the allen screw which holds the lock in place,unscrew it and remove the lock;if the spindle is attached i'm wrong and you need to look elsewhere; if the spindle is not attached it will be
hanging loose in the internal locking mechanism,carefully remove it with pointed nosed pliers ;it should just pull out; do not drop it or you will have to get a replacement or dismantle the door to retrieve it. You can then refix the spindle with a replacement roll pin or preferably a split pin ;which won't fall out in future; and reassemble the lock to the door.
Hopefully problem solved.
Geo.