How to use the @uifabric/date-time.DateRangeType.Month function in @uifabric/date-time

this.setState((prevState: ICalendarInlineExampleState) => {
      const selectedDate = prevState.selectedDate || new Date();
      const dateRangeArray = getDateRangeArray(selectedDate, this.props.dateRangeType!, DayOfWeek.Sunday);

      let subtractFrom = dateRangeArray[0];
      let daysToSubtract = dateRangeArray.length;

      if (this.props.dateRangeType === DateRangeType.Month) {
        subtractFrom = new Date(subtractFrom.getFullYear(), subtractFrom.getMonth(), 1);
        daysToSubtract = 1;
      }

      const newSelectedDate = addDays(subtractFrom, -daysToSubtract);

      return {
        selectedDate: newSelectedDate
      };
    });
  }