Datetimepicker两个选项从下拉列表或manualy ovewrite中选择日期

I'm making a datetimepicker which can save the date by selecting a "pay" date from a dropdown menu and it also should be enable to save the date by manualy clicking a date on the calandar and after that it will be saved in a db. The manual option always has to override the dates from the dropdown.I'm making a datetimepicker which can save the