The standard free start is not a subscription, so there is nothing to cancel and nothing that can charge you. If you took a landing-page offer with the separate card-backed 7-day Starter trial, this is how to stop it.
- Open Profile then Billing.
- Find your trial in the plan section.
- Choose to cancel.
- Confirm. The screen tells you the date access ends.
Cancelling stops the renewal. It does not lock you out on the spot: the app and any credits you already have stay usable until the trial period ends, so cancelling on day two still leaves you five days to finish evaluating.