Close Bootstrap Modal Popup on ASP.Net GridView Select Button click using C#

How to close the popup gridview after textbox bind in asp.net?

As this is my coding

txtval1.Text = GridView1.SelectedRow.Cells[1].Text;
txtval2.Text = GridView1.SelectedRow.Cells[12].Text;
txtval3.Text = GridView1.SelectedRow.Cells[0].Text;

<div class="modal fade" id="myModal" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
    <div class="modal-dialog">
        <asp:UpdatePanel ID="upModal" runat="server" ChildrenAsTriggers="false" UpdateMode="Conditional" >
            <ContentTemplate>
                <div class="modal-content">
                    <div class="modal-header">
                        <h4 class="modal-title"><asp:Label ID="lblModalTitle" runat="server" Text=""></asp:Label></h4>
                        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
                    </div>
                    <div class="modal-body">
                    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnSelectedIndexChanged="GridView1_SelectedIndexChanged"  cellpadding="12" class="table table-bordered table-hover">
                        <Columns>
                    <asp:BoundField DataField="EmployeeID" HeaderText="EmployeeID" />
                    <asp:BoundField DataField="Name" HeaderText="Name" />
                    <asp:BoundField DataField="Last_Name" HeaderText="Last_Name" />
                    <asp:BoundField DataField="First_Name" HeaderText="First_Name" />
                    <asp:BoundField DataField="Middle_Name" HeaderText="Middle_Name" />
                        
                    <asp:CommandField ShowEditButton="True" />
                    <asp:CommandField ShowSelectButton="True" />
                    <asp:CommandField ShowDeleteButton="True" />
                    </Columns>
                    </asp:GridView>
                    </div>
                    <div class="modal-footer">
                        <button class="btn btn-info" data-dismiss="modal" aria-hidden="true">Close</button>
                    </div>
                </div>
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>
</div>