The update can take up to 10 minutes. To update successfully: Ensure your TV is powered on. Ensure the Chromecast is tightly plugged into the HDMI input in your TV. Ensure the Chromecast is tightly connected to the power supply and the power supply is plugged into the wall outlet.
Confirm your setup device can connect to Chromecast. Move the setup device closer to the Chromecast. Check that the Chromecast is listed as an available wifi network under the Network Settings of the setup device. If the Chromecast is listed as an available Wi-Fi network, connect to that network and attempt setup again.