simply guitar subscription

hi, i purchased the premium subscription of simply guitar directly on the website and i don’t know how to cancel it. since i didn’t go through the process via the app store and that i did it on the website, when i go to settings on my iphone, then click on my name and then click on subscriptions the subscription to simply guitar doesn’t appear. i am still on the free trial time but i would really like to cancel my subscription before it ends. can someone please help me ? thank you