Make a copy of the 'data.win' file somewhere else on your computer, then change the name of that file to 'game.droid' the right-click on it then 'Cut'. In the Undertale folder you will see a file called 'data.win', if you don't see it, then scroll down. If you installed Undertale from Steam then while you are in Steam right-click the name 'Undertale' in installed games then, Properties, 'Browse Local Files'.
Next, open your 'Undertale' folder from C:\Program Files\Undertale\. Go to the '/assets' folder, you will see a file called 'game.droid', this is the file which contains everything from the game(or should contain) (code, graphics, sfx, etc). Now, right-click the blank file we downloaded earlier(UndertaleWrapper.apk) then hover over the bar that reads '7-Zip', then click 'Open Archive'.
