The feature is only intended to be used by developers testing their Android Studio projects locally, so you have to install the Linux environment, set up ADB inside of Linux, enable ADB from the Android settings on your Chromebook, and finally install the APK through ADB. We have full instructions
here if you're interested, but the process still
adds a "This device may contain apps that haven't been verified by Google" message to your Chromebook's lock screen.