Please checkout our other blog for general instructions:

https://shop.nidici.com/index.php?route=blog/article&article_id=7

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