Thanks for reaching out. I want to understand your concern further.
A few questions: Is the Chromecast already set up and connected to your network? What's the LED light status in your Chromecast (2nd gen) (solid or blinking white light)? Are you getting a message "No devices found" when trying to cast a video from a Chromecast-enabled app and does it show as unavailable in the Google Home app?
Try these steps: