how to close form 2 from form1 click button in windows form using c#

Try the below code:

private void Button_Click(object sender, EventArgs e)
{
    Form formToClose = null;

    foreach (Form form in Application.OpenForms)
    {
        if (form is Form2)
        {
            formToClose = form;
            break; // Exit the loop once Form2 is found
        }
    }

    if (formToClose != null)
    {
        formToClose.Close();
    }
}