Once you have the correct scatter file, flashing is straightforward.
[SYSTEM] SYSTEM_LOADADDR = 0x15000000 SYSTEM_FILE = system.img
[SECRO] SECRO_LOADADDR = 0x14000000 SECRO_FILE = secro.img
I'm assuming you are looking for a proper story or information related to the MT6769 Scatter File Download. Here's what I found: