You can cancel your free trial through your iTunes settings in the following way:
1. Open the iTunes app and and click on the profile picture.
2. Select your Apple ID.
3. Scroll down through the options and click on the 'Subscriptions' button.
4. Locate your Blinkist subscription and click on 'Cancel Trial'.
5.Click on 'Confirm' to confirm the cancellation.
6. This is how the subscription looks when it has been successfully cancelled. There is no 'Cancel Trial' option, it shows the expiry date and the only option is to resubscribe.