Usually,there is a spring in side the switch,which looks like it failed.looks like you need a new switch pack,does the switch still work? You could open Older fiat switches up and do minor repairs,but unsure with this type of switch.
Thank you for your answer! The problem was that, as in the photo, the plastic “bracket” for the switch panel’s screw is broken, it has fix with glue, so the switch panel is not in its correct place.