How to split Robot model into individual movable joints

Hello, I have a STP 3D file from the original robot manufacture that I would like to split or separate into the 6 joints, with each joint being able to move clockwise & counter-clockwise the same as the real robot does, still attached to each other but able to freely rotate with separating away from each other.

I specifically want to use this model as it matches the real welding robot that I have.

I have looked up a few methods online and tried a few of them without success, unfortunately I only have Freecad & Onshape to use. In Freecad the model loads and the tree view on the left shows up as the model loads, but as soon as it is finishing fully loading the tree view disappears so not possible to do.

I have attached the STP file for reference.

Any suggestions on the best way to achieve this would be greatly appreciated.

Thanks, Terry