public static frmRe_Appointment getForm()
 {
     if (form == null)
     {
         form = new frmRe_Appointment();
     }
     return form;
 }
 private void btnReAppoinment_Click(object sender, EventArgs e)
 {
     frmRe_Appointment formReAppointment = new frmRe_Appointment();
     formReAppointment.Show();
 }