You mean while playing? The + to the left of the volume button adds it your library. Or you click the ... button to the right to have the options to add/remove to library, like or dislike.
Yes that is the one I meant, it was only showing the volume bar. I dunno if it was because I changed back from another country´s store, or if it was because I restarted the Watch, but now it is working as it used to.