Calendar.jsx

....
import {
  format,
  startOfWeek,
  addDays,
  startOfMonth,
  endOfMonth,
  endOfWeek,
  isSameMonth,
  isSameDay,
  subMonths,
  addMonths
} from "date-fns";

const Calendar = () => {
....
   const getHeader = () => {
    return (
      <div class="header">
        <div
          className="todayButton"
          onClick={() => {
            setSelectedDate(new Date());
            setActiveDate(new Date());
          }}
        >
          Today
        </div>
        <AiOutlineLeft
          className="navIcon"
          onClick={() => setActiveDate(subMonths(activeDate, 1))}
        />
        <AiOutlineRight
          className="navIcon"
          onClick={() => setActiveDate(addMonths(activeDate, 1))}
        />
        <h2 className="currentMonth">{format(activeDate, "MMMM yyyy")}</h2>
      </div>
    );
  };

....
}