If the power cut out during an update and the router no longer boots, there is no easy software fix. The device will likely require hardware repair (serial cable flashing) or replacement.
LTE download speeds up to 150Mbps, SMS functionality, and improved WLAN security [3, 6]. Important Safety Warning huawei b311221 firmware download link
Rather than searching for external download links, which carry security risks like malware or "bricking" your device, experts recommend using official Huawei methods: If the power cut out during an update