I can do this on desktop and on iOS devices but can't find an option on the Android app. I'm on the latest version (126.96.36.1993) so am I missing something or is this not implemented in the Android version yet?
You can't upload your local files to spotify. You can download them from your PC to your mobile device and the steps for doing that are in the link I posted. If you mean something else, please explain in more detail, thanks.