Step by step To Flash Firmware BY SP FlashTool:
Download MTK Driver From Here then install on your PC.
Downlaod SP FlashTool From Here then install on your PC.
Turn off your Android device and remove the battery (if it is removable).
open Flash_tool.exe then A window will appear Smart Phone Flash Tool, then click on the Download tab.
click on the button Scatter-loading.
Now, navigate to File Scatter (normally exist in a folder Stock ROM or Custom ROM).
click on the Download button to start the process
Now, connect your Android device to your computer using a USB cable
Once connected, now press and hold the Volume Down or Volume Up, so the computer will easily detect your Android device.
If the flashing process is completed properly, will appear Green Circle