Moving element through curves to right an left site

Hi at all, I am a beginner in grasshopper and it is a very complex programme. So I am at the end of my knowledge. I would transform an element through attractor curves. My element has an axis which should move on the right site of the curve to right and on the left site to left. You can see it at the picture.At the moment the axis is moving in one way. I cannot find a panel where I can move it in both sites. In the attachment is the Rhino document and the grasshopper set up.

Has somebody an idea which can help me with this problem?

Thanks in advance.