Fix an Android Application

I'm trying to update an android game I made, but I'm new to Android Studio and can't figure out how to update the .apk file. I need someone that can fix the code for me. It should be very simple for someone that knows what they're doing. In addition to fixing the code and creating the new .apk file, I'd like you to write up some instructions for me so I can do it on my own next time.