How to SELECT a drop down list item by value programatically in C#.NET?
If you know that the dropdownlist contains the value you're looking to select, use:
ddl.SelectedValue = "2";
If you're not sure if the value exists, use (or you'll get a null reference exception):
ListItem selectedListItem = ddl.Items.FindByValue("2");
if (selectedListItem != null)
{
selectedListItem.Selected = true;
}