How to save database output to a file in D drive using c#

i want to display or save the output in a particular folder/file. But can't understand how to do.
Here's the code where i blocked. Help me.
private void button1_Click(object sender, EventArgs e)

        {

                              

            sql = "select * from booking where b_no='" + textBox1.Text + "'";

            ds = new DataSet();

            ds = DataGetSet.GetData(sql);

            for (i = 0; i < ds.Tables[0].Rows.Count; i++)

             {

                label3.Text = ds.Tables[0].Rows[i][1].ToString();

                label4.Text = ds.Tables[0].Rows[i][2].ToString();

                label5.Text = ds.Tables[0].Rows[i][3].ToString();
             }
        }