As of now it’s not possible to cancel your subscription from within the Android app. If you’re sure you want to say goodbye, log in to your account at Funimation.com or you can go to the Google Play app and follow the instructions:
• At the top right, tap the profile icon.
• Tap Payments & subscriptions. Subscriptions.
• Select the subscription you want to cancel.
• Tap Cancel subscription.
• Follow the instructions.