Sure! You can do it directly with the company you bought koala from.
Apple
With Apple, you have 30 days to claim your refund – here are the instructions. https://support.apple.com/en-gb/HT204084
If you’re on android, you only have 48 hours to get a refund directly with them – here are the instructions: https://support.google.com/googleplay/answer/2479637 – if it’s been more than 48 hours, please get in touch directly with me, and I may be able to process the refund.
PS: if you ask for too many refunds through Apple or Google, they can start to refuse (as they probably suspect you’re using the App Store as a lending library rather than a store). There is nothing I can do to change Apple or Google’s mind about those decisions.