Time Limit to issue credit note.

There is no specific limit prescribed under GST laws or rules for the issuance of credit notes. 

For Example, One Registered buyer who bought goods from One Registered Seller on FY 2020-21. Now due to some issues he is closing his business and returning all the stocks to Seller. In this case what to do if we found any Goods which were sold in FY 2020-21 and how to issue a Credit Note for those goods ?