Import Excel file to Datagridview in C# or VB.Net

hi i have excel file with following fields name,mobileNo,TotalCoupen.i want to import these field in datagridview with unique serial no.if a person have total 5 coupen it will show 5 coupen serial like (10001,10002,10003,10004,10005) i also attach image

here is my code this code load excel file successfuly but not generate coupen no it only import excel file

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Linq;
 using System.Text;
 using System.Windows.Forms;
 using System.IO;
 using System.Data.SqlClient;
 using System.Configuration;
 using System.Data.OleDb;
 using Excel = Microsoft.Office.Interop.Excel;

 namespace ReadExcelFileApp
 {
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        dataGridView1.Visible = false;
    }

    private void btnChoose_Click(object sender, EventArgs e)
    {
        string filePath = string.Empty;
        string fileExt = string.Empty;
        OpenFileDialog file = new OpenFileDialog();//open dialog to choose file
        if (file.ShowDialog() == System.Windows.Forms.DialogResult.OK)//if there is a file choosen by the user
        {
            filePath = file.FileName;//get the path of the file
            fileExt = Path.GetExtension(filePath);//get the file extension
            if (fileExt.CompareTo(".xls") == 0 || fileExt.CompareTo(".xlsx") == 0)
            {
                try
                {
                    DataTable dtExcel = new DataTable();
                    dtExcel = ReadExcel(filePath, fileExt);//read excel file
                    dataGridView1.Visible = true;
                    dataGridView1.DataSource = dtExcel;
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message.ToString());
                }
            }
            else
            {
                MessageBox.Show("Please choose .xls or .xlsx file only.", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Error);//custom messageBox to show error
            }
        }
    }

    private void btnClose_Click(object sender, EventArgs e)
    {
        this.Close();//to close the window(Form1)
    }

    public DataTable ReadExcel(string fileName, string fileExt)
    {
        string conn = string.Empty;
        DataTable dtexcel = new DataTable();
        if (fileExt.CompareTo(".xls") == 0)//compare the extension of the file
            conn = @"provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + fileName + ";Extended Properties='Excel 8.0;HRD=Yes;IMEX=1';";//for below excel 2007
        else
            conn = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + fileName + ";Extended Properties='Excel 12.0;HDR=Yes;IMEX=1';";//for above excel 2007
        using (OleDbConnection con = new OleDbConnection(conn))
        {
            try
            {
                OleDbDataAdapter oleAdpt = new OleDbDataAdapter("select * from [Sheet1$]", con);//here we read data from sheet1
                oleAdpt.Fill(dtexcel);//fill excel data into dataTable
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message.ToString());
            }
        }
        return dtexcel;
    }
}

}