Credit note

Their is a case that involves a sale transaction between the distributor and big bazaar (customer) in which the sale is recorded by the distributor and a purchase is recorded by the big bazaar. But when comes to payment to the sale transaction  ,the big bazaar is not paying the entire amount. The amount to the sale transaction to the distributor is received after deduction of promotional expenses by the big bazaar . The promotional expenses is received by the distributor from the company as the credit note including Gst... Hence, How to give treatment about the credit note issued by the company to distributor in Gst retruns of the distributor?????