Are you trying to create a stereo pair? 

https://support.sonos.com/en-us/article/create-a-stereo-pair

Just go in and move the speaker to the correct room, the ‘old/incorrect’ room will disappear.

Note, however, that a Sonos room can only contain X speakers, depending on what type of setup there is. That shouldn’t stop you from physically putting the two speaker ‘rooms’ in the same space, you just need to group them in the Sonos software.