Trying to re-position left hand using FABRIK Node but it won't move

Hi, I’m trying to use the FABRIK node to hold the left hand of my character on a gun. I watched a bunch of youtube tutorials and looks easy enough but for some reason I can’t click and drag the section thing around like they do in the videos. If I manually do it from the right side then when I play the game the left arm is up in the air lol. Does anyone know what’s going on? I tried using UE4 versions 4.19.2 and 4.20.1 same problem. I saved and compiled a lot, plus restarted the editor a bunch.

UPDATE: I figured it out, I had to make my Boolean for my character blend-space that was using this animation to true in the editor (aim mode), then I was able to adjust it.

Can you explain how you solve it by providing more detail? I faced the same problem now. I cannot moved it with my mouse. Thanks.