Not a good one out there just for UNA sadly. All they give you what to do after your got everything setup on your machine. This will help you on the before  https://reactnative.dev/docs/_getting-started-windows-android.. Not too bad of a guide to follow, Once you get to header 

Running your React Native application-- Then go to https://github.com/unaio/una-mobile-app and follow the steps and commands as they are on page. Once you start the app in CMD prompt then you can load it into Android Studio and go from there. From here you go up to build app and and do signed bundle and fill in the stuff for your JKS file to upload to Google Play and wait on approval. One day I will make a more detailed guide when I have time. Hope this helps though.