You can cancel your Morty Membership subscription at any time. Deleting the app or your account does not cancel your subscription.
Steps
On iOS:
Open the Settings app.
Tap your name.
Tap Subscriptions.
Tap the subscription.
Tap Cancel Subscription. You might need to scroll down to find the Cancel Subscription button.
Upon cancellation your Morty Membership will be active through the remainder of your subscription period.