Payment will be charged to your iTunes account at confirmation of purchase.
For this reason, any refund request will be handled by Apple as well. For security reasons, we do not have any tools to access their billing platform nor your payment details. Apple manage refund requests internally so you will need to submit your request to them directly: https://getsupport.apple.com/
The steps given in the following link might also help you request a refund for a purchase made in the last 24hours: http://www.imore.com/how-to-get-refund-itunes-app-store