Article in English: Make sure to leave it plugged in so that it is able to reset. The Chromecast cannot be reset when it is unplugged. The button is located next to the Micro USB port at the end of the Chromecast dongle. The light on the Chromecast will begin blinking, and your TV screen should display the Chromecast logo and the message "Resetting to factory defaults". After it has been reset, you will need to run through the setup process again before you can use it.

Summary in Vietnamese:
Xác định vị trí của Chromecast trên TV của bạn. Bấm và giữ nút reset. Giữ nút reset 25 giây. Thiết lập Chromecast.