stereo pair era 100

You can adjust the balance slider in the EQ settings.

I’m not sure that you can; maybe adjust the left/right balance?

I am trying to adjust from sonos app for reducing volume from 1 era 100 speaker is that possible while listening to music tru app please help.

What is your issue after adjusting balance slider?

No issue just wonder can i control 1 side of speaker from sonos app to reduce volume while listen to music in living room

If you configure two speakers as a stereo pair, you will just be able to adjust balance to get what you want. 
If the speakers are placed to positions that indicate much more independent listening positions, I recommend configuring them as two separate „rooms“. So you would be able to use them each one separately or together as a group. If grouped you will be able to adjust volume for each one individually. 

A stereo pair plays 2 discrete channels of a left/right stereo signal.  They are meant to be in the same room, equidistant, and at the same volume or it will sound unbalanced.  If one speaker is closer than the other, you can adjust the balance to fit.

If you have stereo paired speakers in 2 different rooms, each room is only getting half of the left/right signal.  The proper way to configure two rooms to play together is to separate the pair to be individual rooms and group them instead.  You can then control the volume in each separately or ungroup if you like.

Ok thank you for replies i understand it now guys much appreciated.