Please checkout our other article for general instructions:
https://iflightrc.freshdesk.com/support/solutions/articles/48001148115-firmware-wiring-factory-dumps
Betaflight unified and legacy targets: https://www.youtube.com/watch?v=n-3vL6Wgumg
How to flash Betaflight 4.1 and above: https://www.youtube.com/watch?v=dvmIVM-2N74