Utilities:

One can import and use these two functions to convert Gregorian date to Jalali date and vice versa.
These functions accept date object as the first argument and divider sign as the second argument ('/' is the default value).

convertToFa( dateObj, '/' )


import DtPicker, {
  convertToFa
} from 'react-calendar-datetime-picker'

const DatePicker = () => {
  const [date, setDate] = useState(null)
  return (
    <div>
      <DtPicker
        onChange={setDate}
      />
      <p>{convertToFa(date)}</p>
    </div>
  )
}
export default DatePicker

value:
null

converted value:
""

convertToEn(dateObj, '-')


import DtPicker, {
  convertToEn
} from 'react-calendar-datetime-picker'

const DatePicker = () => {
  const [date, setDate] = useState(null)
  return (
    <div>
      <DtPicker
        onChange={setDate}
        withTime
        local="fa"
      />
      <p>{convertToEn(date,'-')}</p>
    </div>
  )
}
export default DatePicker

value:
null

converted value:
""