APK building problem

I built an APK file but it didn’t work when I put it on my phone.(VR game using Google VR)
There were a few bugs during my first attempt to build the game, not sure if that’s the cause of it or not. So one of them was “CommandInvokationFailure: Unable to convert classes into dex format.” and I deleted the whole Android folder to solve the problem. After that, I put the APK file on my phone and it crashed when it’s downloading. Please help.

btw, I follow this tutorial.

You need to provide a lot of details

How did it crash?
You say you created the apk put in on the phone and crashed when downloading? Downloading what? Does this imply that it run and you downloaded something through the app?
Android folder == Android SDK or something like Plugin\Android? What did you do after to create the build?