Concentration curl movement can be performed while the person is sitting or standing.
But since the movement is called “concentration”, it means that the biceps must be isolated.
Therefore, it is in my personal opinion that concentration curl is better done sitting down.
Anyway, to start, touch your right elbow on the side of your right and inner knee.
Extend your forearm down and lift the dumbbell.
Curl it up to level with your elbow and then put it back down.
(If you must bend your back to perform the move, do so. Don’t create other movements to cause strain.)