To reskin, it's completely easy!
Every graphics, audios, fonts of this game is located in folder- res.
1. Open source code archive file.
2. Open <App> folder, then go to <src> folder.
3. Go to <main> folder.
4. Go in to <res > folder.
You just need to replace your graphics and audios in these same folder.
Remember you should keep the same name in PNG format!
You can find all arts of this game in folder . (go to App/ src/ main/ res/ drawable)
Exchange your graphics in same name with these one in folder.
If you want to add new mp3 or strings, replace it with audios in folder. (App/ src/ main/ res/ raw)
To change the font or if you want to add new one, go to App/ src/ main/ assets folder and create your own font style.