How to fix internal door release on Ford Focus C-Max (03)?

Hi, my partners ford focus c-max tdci, internal door passenger handle doesn't work properly. the handle functions correctly from the outside, but you really have to pull the handle from inside to open it. its got to the extent now that the casing to the handle is coming away from the door panel. all other doors OK from inside. any suggestions on how to fix it?

really appreciate your responses

thanks