Problem>> How to clear the dropdown value to default in ASP.Net C#?
or
How to reset the dropdown to first value  in ASP.Net C#?

Solution>>  you can use any one of these
Approach 1 ) dropdownlist1.selectedindex=0;
Approach 2  )dropdownlist1.selectedindex = -1
Approach 3 ) DropDownList1.Items.Clear();