Android:
Please click here to request a refund for a subscription on an Android device.
iPhone:
Submitting for a refund, and all billing in general, is done through Apple. You can request a refund when you Report a Problem through the steps found here: https://support.apple.com/en-us/HT204084
You should still be able to get a refund after even if you have the app installed for over 90 days. Apple is the only way to receive a refund from an app purchase. We have no ability to issue a refund from our end. You can see more on how to request a refund here: https://www.imore.com/how-to-get-refund-itunes-app-store