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You can download Sonos for your Mac from here --> https://www.sonos.com/redir/controller_software_mac
Click the above link and a file named SonosDesktopController622.dmg file will be downloaded. Double click on the downloaded file and install it to Applications folder. You can then open it from Applications folder.
(If you don't see the downloaded SonosDesktopController622.dmg file, then click on the Finder icon on dock, then click on Go menu and select Downloads. This will bring Downloads folder. Now you see a file named "SonosDesktopController622.dmg " file there. Double click on it to open)
If you have any difficulty on following the steps above, please let me know and I will continue to help you.