The trial membership can be canceled by going to “Accounts & Lists” on the site. Then choose “Your Prime Membership“. Somewhere below on the page, you will see “Membership Management“. Right under this, “End Trial and Benefits” will be given. You can press this option and the Amazon Prime free trial subscription should no longer be active.
You can see more information about Amazon subscriptions on:- https://www.errorsdoc.com/software/cancel-amazon-subscriptions/