If you would like to request a refund, you will need to contact Apple. This is because all transactions take place via the App Store - we do not process any payments ourselves and therefore we cannot process any refunds ourselves.
To request a refund from Apple, follow the instructions here to report a problem: https://support.apple.com/en-gb/HT204084 and then select the Refund option. Please note that any refund will be at Apple's discretion.
You can find more detailed instructions on how to request a refund here: http://www.imore.com/how-to-get-refund-itunes-app-store