Retrive Value from Dataset

I have added a dataset to my project
and created a tableadapterCategory inside this sql query i created FillByID(@ID)
SELECT        IDCategory FROM            Categories WHERE        (IDCategory = @IDCategory) 
the query should return a number for example 5
I have a button opn click I don t know how to change the selected index of dropdownlist to be equal t o 5
DropDownList.SelectedIndex to be = 5  FillByID(@ID)

please help