Download this Avvio 778 firmware flash file (stock ROM) to un-brick and restore your device to its default, factory state. If you previously rooted or modified the system partition in any way, flashing this stock ROM will overwrite all existing modified system files to replace with factory software.
Ensure to backup all valuable data on the phone, like contacts, messages, app data, etc. This is usually a necessary step before flashing, or resetting your smartphone or tablet. After this process is complete, all data on the device is completely lost.
Again, ensure to charge the phone to at least 30%, so the flashing process is not interrupted by low battery. Interrupting the firmware installation process could result to a dead device.
Download the firmware file from the link below and follow the recommended flashing instructions immediately after the download options. Please report any broken links discovered.
Important! Always backup existing firmware before flashing any other firmware.
How to flash
After downloading the firmware from above link, extract the contents of the archive to an empty folder on your computer. Get a functional USB cable, then follow the instructions via this link to learn how to flash the firmware.
If you have any questions or other contribution please post in comments section for assistance.