ERROR: APK path is not specified for module

1. From your existing project, go to 'File' -> 'Project Structure'
2. Click 'Modules' entry from the 'Project Settings' group (on the left side)
3. Click 'Android' module for your project
4. Click 'New' where it says 'Android Platform'
5. Point it to the Android SDK location that you have locally.
6. Select an API version.
7. Click 'Apply'