To override the function first install the sale module and override the class sale.order and set draft and use feedback function as show in given below code

def feedback(self, cr, uid, data, acquirer_name, context=None):

        tx = None
        res = super(PaymentTransaction, self).form_feedback(cr, uid, data, acquirer_name, context=context)

        # fetch the tx, check its state, confirm the potential SO
        tx_find_method_name = '_%s_form_get_tx_from_data' % acquirer_name
        if hasattr(self, tx_find_method_name):
            tx = getattr(self, tx_find_method_name)(cr, uid, data, context=context)
        if tx and tx.state == 'done' and tx.acquirer_id.auto_confirm == 'at_pay_confirm' and tx.sale_order_id and tx.sale_order_id.state in ['draft', 'sent']:
            self.pool['sale.order'].action_confirm(cr, SUPERUSER_ID, [tx.sale_order_id.id], context=dict(context, send_email=True))
        elif tx and tx.state not in ['cancel'] and tx.sale_order_id and tx.sale_order_id.state in ['draft']:
            self.pool['sale.order'].force_quotation_send(cr, SUPERUSER_ID, [tx.sale_order_id.id], context=context)

        return res