Upgrade features of android quiz game app for which code is in kotlin -- 2

I have an Android quiz game app written in Kotlin and I'm looking for an experienced freelancer to update the features on the app. Specifically, I would like to upgrade the gameplay of the existing app. I already have an idea of how the new gameplay should work and I'm also hoping to add a discover page feature. The other features such as graphics, sound effects, achievements and in-game purchases need to be upgraded. If you have expertise in Kotlin and this kind of development, I'm eager to hear your ideas and see what you can do. The app functions with a backend which calls for the app via API's. Backend is built in php.