A Chromecast factory reset will erase all your settings, accounts, Wi, Fi networks, and personalized files so that your device is like new right out of the box. One way of doing this is through the Google Home app. Open the app on a device that is connected to the same Wi, Fi network as your Chromecast, press and hold your Chromecast device tile, then go to Settings, More, and choose Factory reset. Press OK when prompted and allow your Chromecast to restart and clear all data. If resetting through the app fails, you can try to reset with the hardware button. To do that, keep pressing the physical reset button on Chromecast until the LED light starts flashing, and then release it to give the signal for the device to reset.