I am installing this. After tightening the screw hardly, the big wire still falls out if I pull it a little bit with very small force. I am not sure that I am doing like others would do. Do you have any idea to tighten the wire into that hole? The wire is 105C - 600V, the circuit breaker is 63A
No guessing is allowed.
The breaker's labeling or specification sheet will call out a specific torque you must use. Torque it to that spec. And no other. If you lack the equipment to do so, get it.
I would say look closely inside there while you turn the screw on an empty one, so you have a clear understanding of how the mechanism works. The wire flaring out like that suggests it may be missing the mechanism.
Also, as Programmer66 suggests, make sure that particular hole isn't broken; try another hole.
That I am aware of, it is not to be tightened gently, it needs to be tightened rather snugly, typically there is a torque rating that is given, that will be on the breaker itself, if not on the makers website.
If you are certain that the wire is stripped bare to the correct length, and inserted into the correct spot, and tightened, the wire will not easily pull out, if at all.
That appears to be a rising clamp wire attachment, with these you must fully loosen the screw before inserting the wire, else you risk the wire passing below the clamp jaw and not being connected, or worse only some of the wire strands being clamped and the join overheating.
After insering the wire tighten the screw to the correct torque,