Hi,
I am expert in Android [ kotlin ], [ java ] apps working with quite a few years,
I have read the requirements as you want to change app design like Astrill VPN and some other functionalities setting options.
I can perform changes in your existing Android app for you in accordance with your needs.
So, it's would be extendable latter if you want to add new functionality in your app.
I will provide you a quality work.
Let's chat to proceed.