Hivarun.p,

Check this example. Now please take its reference and correct your code.

I have created the example using the below article.

Merge GridView Cells or Columns in a Row in ASP.Net using C# VB.Net

HTML

<table border="0" cellpadding="0" cellspacing="0">
    <tr>
        <td>
            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" OnDataBound="OnDataBound" Caption="All Records">
                <Columns>
                    <asp:BoundField DataField="Country" HeaderText="Country" />
                    <asp:BoundField DataField="City" HeaderText="City" />
                    <asp:BoundField DataField="ContactName" HeaderText="Name" />
                </Columns>
            </asp:GridView>
        </td>
        <td>&nbsp;</td>
        <td>
            <asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="false" Caption="Merged Records">
                <Columns>
                    <asp:BoundField DataField="Country" HeaderText="Country" />
                    <asp:BoundField DataField="City" HeaderText="City" />
                    <asp:BoundField DataField="ContactName" HeaderText="Name" />
                </Columns>
            </asp:GridView>
        </td>
    </tr>
</table>
<br />
<asp:Button Text="Get Merged" runat="server" OnClick="GetValue" />

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        GridView1.DataSource = GetData("SELECT TOP 9 ContactName, Country, City FROM Customers GROUP BY Country, City, ContactName");
        GridView1.DataBind();
    }
}
private DataTable GetData(string query)
{
    DataTable dt = new DataTable();
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                sda.Fill(dt);
            }
        }
        return dt;
    }
}
protected void OnDataBound(object sender, EventArgs e)
{
    for (int i = GridView1.Rows.Count - 1; i > 0; i--)
    {
        GridViewRow row = GridView1.Rows[i];
        GridViewRow previousRow = GridView1.Rows[i - 1];
        for (int j = 0; j < row.Cells.Count; j++)
        {
            if (row.Cells[j].Text == previousRow.Cells[j].Text)
            {
                if (previousRow.Cells[j].RowSpan == 0)
                {
                    if (row.Cells[j].RowSpan == 0)
                    {
                        previousRow.Cells[j].RowSpan += 2;
                    }
                    else
                    {
                        previousRow.Cells[j].RowSpan = row.Cells[j].RowSpan + 1;
                    }
                    row.Cells[j].Visible = false;
                }
            }
        }
    }
}
protected void GetValue(object sender, EventArgs e)
{
    DataTable dt = GetData("SELECT TOP 1 ContactName, Country, City FROM Customers").Clone();
    foreach (GridViewRow row in GridView1.Rows)
    {
        for (int i = 0; i < GridView1.Columns.Count; i++)
        {
            string contactName = "";
            string country = "";
            string city = "";
            if (row.Cells[i].RowSpan > 0)
            {
                country = row.Cells[0].Text;
                city = row.Cells[1].Text;
                contactName = row.Cells[2].Text;
                dt.Rows.Add(contactName, country, city);
                break;
            }
        }
    }
    GridView2.DataSource = dt;
    GridView2.DataBind();
}

Screenshot