Thank you for answers @Paul A , @John B . Yes, my Sonos Play:1 speaker was already connected to Sonos S2 app so it is apparently upgraded to new system.
EDIT: I just red on sonos forums that If i have S1 setup i can downgrade S2 speakers after factory resetting them and connecting back to S1 system. So If I create a new setup with ZP90 and factory reset my S2 speaker i should be able to downgrade it while connecting to ZP90? Can a new system be setup with only ZP90 in it?
You can make a new system with just the ZP90 on it, sure. Use the S1 app.
You could them factory-reset the Play:1 and add it to the S1-running ZP90 system if you want to.
Note this will lose all configuration and playlists on both systems.