Debit notes

For GST purposes, the supplier will issue the credit note for return of goods.

That CN will reflect in the purchaser GSTR-1 and he will reverse the corresponding ITC in his GSTR-3B.

Debit note issued by the purchaser for purchase return is not a valid document for GST purposes or you can say that it has been issued for accounting purposes only. Such DN is not required to upload in GSTR-1/3B.