If the cardholder has simply changed cards, you can refund to the expired or canceled card. The issuing bank has an obligation to honor the transaction.
If the cardholder has not only changed cards, but also closed their bank account and moved to another bank, you should not attempt to process a refund. Instead, you should liaise with the customer to find another solution like updating the back account details.
Too see the verification documents required to change the bank account, visit this article.