This was a heavily used feature by myself. Also had the option of viewing the album info from a selected song. That’s not working either. 

On the Home Screen, tap the name of your system top left (or drag up the Now Playing section from the bottom of the screen). This brings up all your available speakers/rooms.

Tap the room you want to play in. This becomes the active room.

Select the music you want to play. It will then play in that room/speaker.

This works. Took me forever to figure that one out. Still not finding playlists or any means to scroll through my library without scrolling through every title. There used to be letters on the right hand side to allow easier browsing. The latest app is not much of a step in the right direction (yet, at least).

Although that does work, and you could do the same in the old app. You used to be able to search first, and then choose your speaker. It’s a step down in functionality and want it restored

‘Tap the room you want to play in’

Both rooms are ticked.

Do you untick the room you don’t want and tick the one you do??

If you are ticking rooms, you are in the grouping screen, which will do nothing except group rooms.  Here’s how to switch the “Now Playing” room to something else:

Below: Now Playing room is the Den

I want to play something different in the Bathroom.  Swipe up on the little bar at the top of the Den (Now Playing) room.

Scroll (if needed) to the room you wish to select (Bathroom) and tap anywhere in the highlighted area to select the room.  

Whatever room you tap (ex. Bathroom) is now the default room.  Anything you select for a source above will now play in that room.