Can't change animation in UE4

So I basically took the FPS default idle animation and changed the hands format until it got to a position I liked, then I saved, went in-game and noticed it never changed to what I saved.

So I tried to get the .FBX file into Blender to see if I could change it, but the file I imported transformer itself into little pieces scattered around and I can’t even move them.

Can anyone tell me the most simple and easiest way of just changing the skeleton of the default FPS idle animation?