how to unsubscribe or delete an App

You can cancel the free trial the same way as you cancel a paid subscription. See instructions in If you want to cancel a subscription from Apple - Apple Support

See -> Delete apps on your iPhone, iPad, and iPod touch

Delete apps on your iPhone, iPad, and iPod touch - Apple Support

If you delete an app, it doesn’t cancel in-app subscriptions that you might have. While deleting an app, you might see a Cancel Subscriptions option. Learn how to cancel your subscriptions.

• If you signed up for a free or discounted trial subscription and you don't want to renew it, cancel it at least 24 hours before the trial ends.

Contact Apple Support -> Contact Apple Support for more support and assistance.

Check also: that depends on the subscription of the app. 

Go to App Store, search an app, then you will see 'In-App Purchases a monthly subscription or an annual subscription.

You should look at the conditions of the subscription how to cancel the free trial, check with the app developer.