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 Chromecast built-in terms and conditions. It can be enabled at any point via the Bang & Olufsen app by selecting Product settings - Chromecast built-in.
You can download the Bang & Olufsen app here
To disable Chromecast built-in again, you will need to perform a reset. To reset, please see here.