If the physical buttons or SD card method fail, try official software recovery tools. Install Huawei HiSuite on your PC.

Connect the device to a charger and hold Volume Up for ~15 seconds to enter eRecovery. Select Download latest version and recovery to let the device fetch official firmware over Wi-Fi. 3. For Advanced Users: Repacking Correctly

Obtain the official UPDATE.APP file for the S7-721u model from a reputable source. DLOAD Method:

Press and hold simultaneously.

Select in HiSuite and follow the prompts to download authorized images.