(C#.Net) Windows Application SQL VARCHAR to DateTime in TextBox

DataTable dtTable;
DateTime MyDateTime;
MySqlConnection objCon;
MySqlCommand objCmd;
MySqlDataAdapter dtAdapter;

private void Form1_Load(object sender, EventArgs e)
{
     try
     {
          string strCon = "Server = localhost; User id = root; Password = 1234; Database = warehouse_db; Pooling = false; CharSet = utf8; convert zero datetime = True";
          objCon = new MySqlConnection(strCon);
          objCon.Open();
     }
     catch (Exception ex)
     {
          MessageBox.Show(ex.Message);
     }
}

private void show_date_btn_Click(object sender, EventArgs e)
{
     try
     {
          dtTable = new DataTable();
          objCmd = new MySqlCommand();

          objCmd = objCon.CreateCommand();
          objCmd.CommandText = "SELECT * FROM customer WHERE cus_id = '" + id_txtb.Text + "'";
          objCmd.CommandType = CommandType.Text;

          dtAdapter = new MySqlDataAdapter(objCmd);
          dtAdapter.Fill(dtTable);

          MyDateTime = new DateTime();
          // Customer ID : C000001, Date Active : 10/07/2556
          MyDateTime = DateTime.ParseExact(dtTable.Rows[0]["cus_member_date_active"].ToString(), "dd/MM/yyyy", null);
          date_active_txtb.Text = MyDateTime.ToLongDateString();

          MyDateTime = new DateTime();
          // Customer ID : C000001, Date Expire : 11/08/2556
          MyDateTime = DateTime.ParseExact(dtTable.Rows[0]["cus_member_date_expire"].ToString(), "dd/MM/yyyy", null);
          date_expire_txtb.Text = MyDateTime.ToLongDateString();

          dtTable = null;
     }
     catch (Exception ex)
     {
          MessageBox.Show(ex.Message);
     }
}

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
     try
     {
          objCon.Close();
     }
     catch (Exception ex)
     {
          MessageBox.Show(ex.Message);
     }
}

    ''' <summary>
    ''' Input String format 2555/12/31 08:30:00 AM +7 พ.ศ.
    ''' </summary>
    ''' <param name="thDateTime"></param>
    ''' <param name="dateSeperate"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Shared Function TryParseExactThai2US(ByVal thDateTime As String, Optional ByVal dateSeperate As String = "/") As DateTime
        'Web Server Timezone = US & Canada (-5)
        'web.config/app.config
        '<globalization fileEncoding="utf-8" requestEncoding="utf-8" responseEncoding="utf-8" culture="en-US" uiCulture="en-US" enableClientBasedCulture="false"/>
        Dim thCultureInfo As New System.Globalization.CultureInfo("th-TH") With {.DateTimeFormat = New System.Globalization.DateTimeFormatInfo() With
                                                                                    {
                                                                                     .Calendar = New System.Globalization.ThaiBuddhistCalendar()
                                                                                    }
                                                                                }
        Dim USDateTime As DateTime
        Dim SetDateFormat As String = "yyyy" & dateSeperate & "MM" & dateSeperate & "dd" & " HH:mm:ss tt z g"
        If DateTime.TryParseExact(thDateTime, SetDateFormat, thCultureInfo, Globalization.DateTimeStyles.AdjustToUniversal, USDateTime) Then
            Return USDateTime 'USDateTime.ToString(SetDateFormat)
        Else
            Return Nothing
        End If
    End Function