The drop down date picker can be used in your ui like a regular date picker. Go the prefabs folder and add a dropdown date picker to your scene:
you can use the UI.Text version :
Or the text mesh pro version:
Configuring the drop down
configure the template for the drop down (see customizing the date picker)
Optionally you can configure the drop down properties :
Run the scene
Get the selected date from script
var dropdown = GetComponent<DatePickerDropDownBase>();
DateTime? selectedDate = dropdown.GetSelectedDate();