you can directly call your button click event like this.
btnSubmit_Click(btnSubmit,null);
or using jquery like this..
$(document).ready(function(){
$("[id*='btnSubmit']").click();
});
if you want to call your button click event in your page load you can directly call like
protected void Page_Load(object sender, EventArgs e)
{
btnSubmit_Click(btnSubmit,null);
}