How does one unsubscribed "Speaker & Headphones Connect" app.

If you are being billed through Apple then you will need to cancel through Apple.

Also, you don't open the Speaker & Headphones Connect app to cancel through Apple.

See the instructions in If you want to cancel a subscription from Apple - Apple Support

If they don't work for you, click on the following from that same support article:

Contact Apple Support

There is an Apple article that explains how to cancel subscriptions. Click on the following link: If you want to cancel a subscription from Apple - Apple Support