You can manage your subscription after subscribing to free 7-day trial. The 7-day trial only offer annual pack at the moment but you can immediately change this to auto-renew to monthly by following the instructions below:
- Go to Settings > [your name] > iTunes & App Store.
- Tap your Apple ID at the top of the screen, then tap View Apple ID. You might need to sign in with your Apple ID.
- Scroll to Subscriptions, then tap it.
- Tap the subscription that you want to manage. If you're being charged for a subscription, but you don't see it in your list of subscriptions, it might be billed through someone other than Apple. Learn what to do if you still can’t view your subscription.
- Use the options to manage your subscription. You can choose a different subscription offering, or tap Cancel Subscription to cancel your subscription. If you cancel, your subscription will stop at the end of the current billing cycle.