How do I cancel auto renewal of Apple TV?

Apple TV+ subscriptions auto-renew until canceled.

If you cancel during the trial, then the subscription ends immediately.

If you cancel after the trial, during the fee paying billing cycles, then a canceled subscription continues to be active until the end of the current billing cycle.

If you need a reminder, set an alert in a Calendar program, a few days ahead of the last day of the trial. To avoid new payments, cancel at least 24 hours before the next billing moment.

You can find information on how to cancel Apple Subscriptions which would include Apple TV here