To do this, visit https://play.google.com/store/account and sign into your Google Play account. You should see a list of all the apps associated with your account. Simply scroll down and find the app you wish to get a refund on, click the three vertical dots next to the app's name, and choose "Report a problem". Finally, select "I'd like to request a refund" from the drop-down box, and explain your reason in the text box. Hopefully, they should be able to get you up and running in no time at all.
However, if you're unsure whether you need a refund, feel free to contact us and explain the issue that you're having. We've found that 9 times out of 10, we can resolve any problems you've encountered so that you can continue to enjoy the app!