Insert the key and turn to the accessory position. There's a small hole on the face of the key assembly, insert a paper clip or something simular and continue to rotate key counterclockwise and the lock mechanism should come out. You want key assembly in same position when installing.

If you don't have the key then you will likely need to take a drill and go thru the key opening and progressively work up to same dia. as lock assembly. It's unlikely you will be able to salvage the switch, I have tried it on couple of occasion and not successful, suggestion order switch and key assembly ASAP.