If you have purchased via web app, visit https://triviamaker.com/account page and you can see an option to cancel your existing subscription.
Android app: If you have subscribed to TriviaMaker using the Android application, you can cancel your subscription follow steps as mentioned in https://support.google.com/googleplay/answer/7018481?co=GENIE.Platform%3DAndroid&hl=en
iOS App : If you have subscribed to TriviaMaker using the iOS application, you can cancel your subscription follow steps as mentioned in https://support.apple.com/en-us/HT202039