It won't download
if the game says it doesn't download while it's installing, that means it took too long to download, so Android decided to scrap the idea. Had this happen to me a couple of times when I downloaded some games on my own Android.
if it just won't start the download in general, you'll need to find something to install the app manually. I forget the app I installed to install stuff manually, but you'll need to find it too.