Step 1-First of all download SP Flash Tool and extract inside a folder, you can extract in 'C' drive for batter work.
Step 2-Download and install Vcom driver in your PC, this is a must requirement of SP Flash Tool flashing, without the driver you can’t flash the device.
Step 3-After that download official firmware file.
Step 4-Extract downloaded file inside a folder.
Step 5-Connect your switched off phone to your PC via USB cable then go to SP Flash Tool folder and run 'flash tools.exe' file.
Step 6-Navigate the download tab and then click over 'Load Scatter File', a pop up is now opened, navigate 'Load Scatter File' to downloaded file folder and click OK.
Step 7-Check everything, in custom recovery case check 'Download only' option, and then hit over the download button.
Step 8-Wait for success, a green circle shoold appear. Done.