You can create a SYSTM web subscription rather than manage your account through Apple. If you've previously created a subscription through Apple, you will need to cancel that subscription and wait for it to fully expire before creating a web-based subscription through Wahoo. (see Cancelling your SYSTM subscription on iOS for more details.)
Log into your SYSTM user account at systm.wahoofitness.com, or from a desktop (windows or mac) version of the app, to view and manage your subscription. Follow the instructions found here: Creating and Managing a SYSTM subscription (web, Mac, Windows)
If you still have an Apple subscription that is active, you will see the following screen:
Be sure to allow your subscription to fully expire before proceeding. You will know your subscription is expired when you can no longer play a workout or access content on the app.