how to rotate a bone without affect child bone?

HI,
these day, I need do some work on rotate a bone freely, and I find that when I rotate the parent bone, the child bone will be affected, and child bone can not be rotate correct. any way I can finish this.
more detail, I add oseableMeshComponent, and call “set bone rotation by name” in BP, and I use a hand model. when I rotate the hand , the finger will be affected, thus, I can rotate the finger at the same time . so hope you help me, thanks!