Hi there belsem,

I personally suggest taking these three simple steps:
1. creating a constructor function where the parent component's state would be defined (say, "appointment"), initially pointing at null;
2. there is a handler for an onChange event on the DatePicker, so have it trigger a custom function as a callback (say, onChange={this.handleDateChange});
3. define your handleDateChange callback, say

onChange = (e, date) =>{
    console.log(e);
    console.log(date);
    this.setState({
      appointment: date
    });
}

This would also be where you'd convert the date format as needed, using f.e. moment API (moment(date).format('DD-MM-YYYY')).

Hope it helps.

With Best Regards,
Kuba