Note: If you delete the app, the subscription will not be cancelled!
Cancelling the subscription prevents you from the subsequent charges. However, that doesn't refund your last payment.
To cancel the subscription on the iOS platform, please follow the instructions below:
Open the Settings app on your device;
Tap your name at the top of the screen;
Tap Subscriptions.
Suppose you don't see "Subscriptions," tap "iTunes & App Store" instead. Then tap your Apple ID, tap View Apple ID, sign in, scroll down to Subscriptions, and tap Subscriptions.
Tap the subscription that you want to manage;
Tap Cancel Subscription.
If you don't see Cancel Subscription, the subscription is already cancelled and shouldn't be renewed.