foreach (Control control in this.Controls[0].Controls)
{
if (control is HtmlForm)
{
foreach (Control con in control.Controls)
{
if (con is ContentPlaceHolder)
{
foreach (Control ctrl in con.Controls)
{
string id = ctrl.UniqueID;
if (ctrl is Label)
{
this.TextBox1.Text = "abc";
}
}
}
}
}
}