Thanks for contacting Syncfusion support.
DropDownList is a dataSource control and it doesn’t have any date format option. Based on the update, we suspect that you are using DatePicker control in your project. If so, then you can set format using dateFormat property in DatePicker. Please refer to the following demo and UG links
If we have misunderstood, kindly share us the details on the following to proceed further.
1) Syncfusion control used in your project.
2) Existing code snippet related to EJ controls of your project.
3) Any example screenshot for your requirement (if possible)