Updating data pulled into the form

Question

I have a table where my constant information is stored. I want to replace the city and town names in this fixed table with city and dsitrict names that I pulled from other tables named city and district. But it is sending blank data. I could never understand why.

private void getcity()
{
    if (conn.State == ConnectionState.Closed)
    {
        conn.Open();
    }    
    OleDbCommand cmd = new OleDbCommand("select * from city ORDER BY id ASC", conn);
    OleDbDataReader dr = cmd.ExecuteReader();
    while (dr.Read())
    {
        comboBox1.Items.Add(dr["sehir"].ToString());
        comboBox1.ValueMember = (dr["id"].ToString());
     }
}

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (comboBox1.SelectedIndex != -1)
    {
        DataTable dt = new DataTable();
        OleDbDataAdapter da = new OleDbDataAdapter("select * from ilceler where city= " + comboBox1.SelectedValue, conn);
        da.Fill(dt);
        comboBox2.ValueMember = "id";
        comboBox2.DisplayMember = "town";
        comboBox2.DataSource = dt;
    }
}