@LeTuan 

Hi,
Typically, the camera will reconnect to the same Wi-Fi network after a power failure or restart. If it doesn't, try the following steps to resolve the issue:
    1. Restart the router, then reboot the camera once the router's Wi-Fi is operational.
    2. Disable the Smart Connect function on the router.
    3. Set Different Wi-Fi names for 2.4GHz and 5GHz Bands.
Then you can check if the camera will reconnect to the router's Wi-Fi automatically.
Best Regards