how do you cancel a free trial that does not show up in subscriptions

See step 4 in the support document you posted from:

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

The blue text is a link, click it for more directions.

In short, you would need to determine wether you actually started that subscription, or somebody else did if you are part of Family sharing, and if you started said subscription on an Apple device, or on a different device or directly on the website of the subscription in question.

Stopappnow240 wrote:

I want to discontinue an apple app during trial period

Follow the steps here: link-> How to cancel a subscription from Apple - Apple Support

I want to discontinue an apple app during trial period