To cancel your subscription, open Cycles and go to the 'Me' section. Tap the 'Settings' icon in the top right corner, and then tap on Cycles Premium. From here, tap 'Manage Subscription', which will take you to your subscription settings where you can cancel.
Alternatively, you can cancel directly from your phone Settings. To do this, open the Settings app and tap your profile photo. Next, tap Subscriptions, find Cycles in the list and cancel your subscription.
If you don't want to subscribe after the free trial, please remember to cancel at least 24 hours before it expires.