You can request a refund within 48 hours after a new purchase or after a payment for renewal, by visiting the Google Play site below:
https://support.google.com/googleplay/workflow/9813244?hl=en 

If 48 hours or more have passed since your order or payment, please send us an email using Email Support below, explaining why you no longer wish to continue your KineMaster subscription. We will let you know if your request meets the conditions for a refund.