The first thing you need to know is: uninstall the app will NOT automatically stop your subscription.You must cancel the subscription manually.
If you uninstall our app but don't cancel your subscription first, you will still be charged by Apple.

The manual​ cancellation steps:

1. Open Settings on your device
2. Choose iTunes & App Store
3. Click the Apple ID: xxxxx@xxxx and choose View Apple ID
4. Click manage under subscription view to stop the subscription

Still can't understand, please visit https://support.apple.com/HT202039 to learn how to manage your Apple subscriptions.