how to get date in rasa

class LeaveForm(FormAction):

    def name(self) -> Text:
        return "leave_form"

    @staticmethod
    def required_slots(tracker: Tracker) -> List[Text]:
        return ['start_date', 'end_date']

    def validate_start_date(self,
        value: Text,
        dispatcher: CollectingDispatcher,
        tracker: Tracker,
        domain: Dict[Text, Any],
    ) -> Optional[Text]:
        # Check if value is a Duckling date-range.
        if isinstance(value, dict):
            # Since both the fields are populated, the form 
            # will no longer prompt the user separately for the end_date
            return {
                'start_date': value['from'],
                'end_date': value['to']
            }
        else:
            return {
                'start_date': value
            }

    def slot_mappings(self) -> Dict[Text, Union[Dict, List[Dict]]]:
        return {
            "start_date": self.from_entity(entity="time"),
            "end_date": self.from_entity(entity="time")
        }

    def submit(self, dispatcher: CollectingDispatcher,
               tracker: Tracker,
               domain: Dict[Text, Any]) -> List[Dict]:
        dispatcher.utter_template('utter_submit', tracker)
        return []