How do I cancel just Apple TV

See the instructions in How to cancel a subscription from Apple - Apple Support or use an internet browser to cancel as described in How to cancel Apple TV+ - Apple Support

If you use instructions in How to cancel a subscription from Apple - Apple Support be sure to note the following from that article:

4-Tap the subscription that you want to manage. Don't see the subscription that you're looking for?

5-Tap Cancel Subscription. (Or if you want to cancel Apple One but keep some subscriptions, tap Choose Individual Services.) If you don’t see Cancel, the subscription is already canceled and won't renew.

Follow the steps in the support document you posted from and select just the Apple TV+ subscription from your list of active subscriptions. Then click on the Cancel button for it.