Find a coach and get 1 on 1 lessons.
I don’t know how to do it in Malaysia, but in England the Badminton England website has a “find a coach” webpage.
Without seeing you play, I can’t suggest much but remember the key points for good drop shots and backhands.
Same overhead preparation (how your body looks from above the waist) as the smash or clear.
Relaxed forehand grip
Get behind the shuttle using a split step (mini squat) and chassé steps ending on your racquet leg.
Have a high point of contact. Hold your racquet above your head straight, then move your arm about 15 degrees forward. That is about where you want to make contact with it.
You want the shuttle to land tight with the net and infront of the service line. If it’s beyond the service line it isn’t as effective as it could be.
Don’t overuse the drop shot. It’s best used when the opponents are defending deep and expecting a smash.
Every forehand shot you can imagine could also be played as a backhand (clear, smash, kill, drive, net shot etc). So be specific about what backhand shot(s) you are struggling with.
Have a loose grip when approaching the shot. Tighten as you hit the shuttle if required (backhand clear).
If you are struggling with the backhand clear, practice the timing and footwork. And remember that you need to adjust your grip the further behind your body the shuttle is. If the shuttle is infront of your body, backhand grip. But if it is in line with your body, adjust to a bevel grip and if it is behind your body, you need a panhandle grip.
The reason you have to adjust the grip is to ensure the strings are pointing in the direction you want the shuttle to travel.
Good luck, it’s never too late to learn badminton things