The only way I know is the standard way, using a backhand thumb grip and slightly pushing the racket forward, as is taught in the videos by BadmintonFamly and other coaching channels. But then I see the Korean player at 1:00 pushing racket-head forward AND turning it around (maybe by supinating his forearm...IDK). Check the video in slow-motion at 1:00. Can someone guide me to the finer details of this method of low serve, and also its pros and cons? If there is a video out there about this style of backhand low serve. I would highly appreciate it.
You mean from this position? Turning your racket under the shuttle makes the contact longer which is positive. And you don't serve to the net so easily. But I felt awkward to start the serve.
Are you talking about a "spin serve"? If so, it's all covered in the video. They talk about when to use it and why to use it and how to do it.