Because Apple manages all subscriptions purchased through the App Store, you'll need to follow these instructions on your iPhone in order to cancel your subscription:
Go to Settings on your iPhone
Tap Your Name at the top of the screen
Find the Dipsea subscription
Choose a different subscription option or tap Cancel Subscription. If you don’t see Cancel Subscription, the subscription is already canceled and won't renew.
If you're being charged for a subscription, but don't see it in your list of subscriptions, make sure that you're signed in with the Apple ID with which you originally subscribed to Dipsea. If this is the case, you may also have purchased your Dipsea subscription via the Dipsea website rather than the App Store. Learn how to cancel a subscription purchased via the Dipsea website here.
To cancel a subscription purchased on an Android device, click here.