How do you fix passenger door lock on a 2000reg fabia classic?

The first step to any successful and efficient repair is diagnosis. You have to determine what the fault is. The process to repair a faulty lock tumbler is a bit different from the process to R/R linkages in the assembly, or any other problem which may be the cause of the fault. There's no way to ensure we give you the correct procedure to repair it without knowing what exactly it is which needs to be repaired.