Once Beosound 1 is connected to your network via Wi-Fi or Ethernet, use the Bang & Olufsen app on your mobile device to access the settings of the product and accept the Google Cast terms and conditions. It can be enabled at any point via the Bang & Olufsen app by selecting Product settings - Google Cast.
You can download the Bang & Olufsen app here
To disable Google Cast again, you will need to perform a reset. To reset, please see here.