You can cancel the automatic renewal of subscriptions that were purchased through the mobile apps in the corresponding store. More details on how to do this can be found here: Google Play Help and Apple Support.
When you cancel the automatic renewal you’ll still be able to use your subscription for the time you’ve already paid. After that, the subscription will be canceled. The payment and cancellation dates are available in the App Settings -> Subscription, or in the app of the corresponding store.
The trial period can be taken only once, therefore if after canceling the trial period you decide to renew your subscription, the payment for it will be taken immediately.
You can renew the subscription at any time before its automatic renewal or purchase a different plan, then the automatic renewal will be enabled automatically.