How do I get a refund for an app that I purchased?

This is primarily a user-to-user support forum; other Apple users like you. There is an Apple article with information about requesting refunds. Click on the following link: Request a refund for apps or content that you bought from Apple - Apple Support

All you can do is try by using the provided link. For the most part, all transactions are final in the App Store, but in some cases Apple will provide a compassionate refund. Some apps offer a Free Trial to see if you like it before you are charged for a subscription, but you will want to make sure that you cancel the free trial at least 24 hours before the trial period ends to avoid a charge. For apps that don't offer a free trial, you will be charged immediately to use the app and cannot expect to create you own free trial for those app by getting a refund later if you do not like it.