If he subscribed to it then it has to be canceled from his account.
This support article explains how to cancel a subscription from Apple on an Apple mobile device, Mac, PC, and online ➔ If you want to cancel a subscription from Apple - Apple Support
Notes:
• You might need to scroll down to find the Cancel Subscription button.
• If you don’t see Cancel Subscription, then the subscription is already canceled and won't renew. An "Expires" date (instead of "Renews") means the current subscription has been canceled but will work until the expiration date. "Resubscribe" (or Renew) is just in case you change your mind about having it end.
• Deleting an app does not cancel a subscription.
• If you don’t cancel trials more than 24 hours before your renewal date, your subscription might renew.
• If you don't have an Apple device, see the options near the bottom of the support document.
• Many subscriptions are set to renew automatically until you intentionally cancel them.
If you can’t find the subscription that you want to cancel, use this shortcut to jump to the section about what to do. --> If you want to cancel a subscription from Apple - Apple Support
If this is a subscription not made through Apple, read—> https://support.apple.com/kb/HT207865
If you still can't find a subscription or still have problems, contact Apple Support using this issue-specific link at the end of the section. --> https://getsupport.apple.com/?caller=kbase&PGF=PGF63006&category_id=SC0060&symptom_id=23208
Scroll down to where you can request a chat session or a phone call.
Alternatively, see a list of Apple phone numbers around the world ➔ Contact Apple for support and service - Apple Support
