Central locking locks but doesn't unlock
 

hello, I have just moved to Nicaragua and bought a 2003 montero sport se . I was given one key which only opens the drivers door (and ignition). The buttons on the driver and passenger door will lock all the doors but not unlock them (only driver doorike the key). Although I can hear a clunk on all doors but they won't unlock. I'm new to Mitsubishi and Nicaragua so grateful for any advice?