Refunds for Klarna and Clearpay orders are handled directly through each provider. You can find full details on their refund processes here:
Klarna:
https://www.klarna.com/uk/customer-service/how-long-do-refunds-take/
Clearpay:
https://help.clearpay.co.uk/hc/en-gb/articles/900005336103-How-do-refunds-work-at-Clearpay