Downloading expansion from google

Working on a mobile game.
I have reviewed the documents and seen all the nodes.

I have signed the APK and have the google developer profile etc.

Only problem I am having is I have no idea how to tell the engine to request the content from the google play store.
Also not 100% sure on how to verify if the content is already installed first.

I would appreciate if anyone could point me in the direction for that.
I presume I have to somehow check the files for the build number, then it will query the store and accept the unique link?