how to fix this problem

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using MySql.Data.MySqlClient;

namespace SSG
{
    public partial class frmBusiness_Statement : Form
    {
        string[,] Plans;
        int BranchId = 0;
        string branchname = "";
        string memberid = "";
        int statementid = 0;
        double TotalRecieptAmount = 0.0;

        public frmBusiness_Statement()
        {
            InitializeComponent();
        }

        private void txtCustomerId_TextChanged(object sender, EventArgs e)
        {
            if (txtCustomerId.Text.Trim() != "")
            {
                try
                {
                    using (MySqlConnection con = new MySqlConnection(GlobalVariables.ConnectionString))
                    {
                        con.Open();
                        /* Have to make change here */
                        string qry;
                        if (cmbPlan.Text == "SID")
                        {
                            qry = "SELECT accountname,tableno,refererid,investment,dateofexpiry FROM investers_sid WHERE investeridsid";
                        }
                        else if (cmbPlan.Text == "RUC")
                        {
                            qry = "SELECT accountname,tableno,refererid,investment,dateofexpiry FROM investers_ruc WHERE investeridruc";
                        }
                        else if (cmbPlan.Text == "PS")
                        {
                            qry = "SELECT accountname,tableno,refererid,investment,dateofexpiry FROM investers_ps WHERE investeridps";
                        }
                        MySqlCommand cmd = new MySqlCommand(qry, con);
                        MySqlDataReader r = cmd.ExecuteReader();
                        if (r.HasRows)
                        {
                            r.Read();
                            txtIvestorName.Text = r.GetString("accountname");
                            txtTableNo.Text = r.GetString("tableno");
                            txtRMemberId.Text = r.GetString("refereid");
                            txtRAmount.Text = r.GetString("investment");
                            dtpClosingDate.Value = r.GetDateTime("dateofexpiry");
                            FillHistory();
                        }
                        else
                        {
                            txtIvestorName.Text = "";
                            txtTableNo.Text = "";
                            txtRMemberId.Text = "";
                            txtLateFee.Text = "0";
                            txtRAmount.Text = "";
                            dtpClosingDate.Value = DateTime.Now;
                            dgInvestorHistory.DataSource = null;
                        }
                    }
                }
                catch (MySqlException ex)
                {
                    MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
            }
        }
    }
}