Your subscription is managed in the respective store that you subscribed in. For example, if you downloaded on an Android device, your subscription is managed with the Google Play Store. If you downloaded on an Apple device, your subscription is managed with Apple's App Store.
For Apple, see here:
For Android, see here:
Also, if you wouldn't mind sharing, could you let us know the reason why you want to cancel and what we can improve on to earn your business?