From the post title, sale it sounds like very complicated shot to make in badminton. If you follow coach Nghia Tran
To hit a backhand shot, health start with a proper backhand overhead grip.
Start off with a proper backhand overhead grip Which means your thumb is at the edge of the racket There should be a groove between the two flat ends.
This allow the wrist to snap without any restrictions. Have your elbow pointing at the shuttle when you want to hit this shot. The head of the racket is above of your lefthand shoulder.
Extend your arm and snap your wrist at the highest point of the shuttle.