Subscription provider rebate for termination of service

An application/streaming service I purchased a subscription for through the App Store has notified me that they will stop the service and deactivate the app on December 19, 2023. (see https://help.globalcyclingnetwork.com/hc/en-gb/articles/19965721079697-What-s-happening-to-GCN-)

The developer/provider has indicated they will be providing a pro-rated rebate for outstanding service via the mechanism of original payment...

"Refund note: You’ll receive a refund to your original payment method for the time remaining on your GCN+ subscription. Refund times may vary by provider. If you have questions, please contact the company who bills you for GCN+, i.e., Apple, Google, or GCN."

I searched online and cannot find any information about how such a rebate will be processed by Apple/App Store?

Where is that information located?