//button event for 'Exisiting' button
        private void btnExisting_Click(object sender, EventArgs e)
        {
            //create instance of form
            frmExistingCustomer Existing = new frmExistingCustomer();

            //display form
            Existing.Show();
        }
 //button event for 'Exisiting' button
 private void btnExisting_Click(object sender, EventArgs e)
 {
     //create instance of form
     frmExistingCustomer Existing = new frmExistingCustomer();
     //display form
     Existing.Show();
 }