On this page, you will find the official link to download Gionee T520 Stock Firmware ROM (flash file) from GoogleDrive. Firmware comes in a zip package, which contains Flash File, Flash Tool, Driver and How-to Manual.
How to Flash
Step 1: Download and extract the stock firmware on your computer.
Step 2: After extracting you will find the Firmware.
[*] Take a Backup of your personal data before flashing or installing the firmware on your smartphone. As this helps you to recover the personal data whenever any thing wrong happens.