If you'd like to manage, change, or cancel your Dispo MAX subscription, you can do so within the native Subscriptions panel in iOS.
Please follow this guide from Apple on where to access your Subscriptions: https://support.apple.com/guide/iphone/manage-purchases-subscriptions-settings-iph3dfd91de/ios
This video will be able to help guide you if you're unable to find it:
Due to Apple's policy, developers are unable to provide refunds for purchases made within the app. The user will need to request to do so here.