Apple's App Store gives us very little control over refunds for in-app purchases from the Apple App Store. All refund requests must go through them.
Customers request refunds in several ways, such as:
Contacting Apple Customer Support and asking for a refund
Logging in and using Apple's self-service tool, reportaproblem.apple.com, to request a refund
Asking their payment method issuer for a refund
You can learn more here: https://support.apple.com/en-us/HT204084
For canceling in-app purchases, please read more here: https://support.apple.com/en-us/HT202039