First download firmware and extract to the PC.
Open Sp flash tool and open it. Browse scatter file.
Now it is ready, if you flash right now its not work, here is the trick.
Open your mobile board and jumper from V-bat to preloader test point.
Now connect phone to the PC and just click on download option. If you get the error change download option to firmware upgrade or format all +Download option and click on download it will start.
Wait for complete, Now it complete and ready to use.
If you select format all +Download option you nee to repair IMEI. To repair IMEI use volcano utility tool.