Go here: https://apps.apple.com/account/subscriptions > tap on 1SE > Cancel Subscription.
Go into your iPhone's Settings > [your name] > iTunes & App Stores > Apple ID > View Apple ID > Subscriptions > 1SE > Cancel Subscription.
Go into the app's Profile tab > Settings (the gear icon at top right corner) > Manage Subscription > Cancel Subscription.
This is the only way Apple allows subscriptions to be canceled.
Note: Cancelling a subscription will not refund any payments you have made. It will only stop you from renewing your subscription. Please talk with Apple for a refund of the remaining time on a subscription.
Here’s a helpful Apple article on it: https://support.apple.com/en-us/HT202039#subscriptions
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