Modify a bluerprint that goes from point A to point B so that he can go from point bo to point a

Hi, I want mesh that goes from point A to point B Along a SplineActor.

By luck I found this marvelous blueprint that seem to work Out, This blueprint is long but this seem to be the part that make it move.

For those who are curious, I find this one there Unreal Engine 4 : Follow Spline Path and Detect Point Interaction - YouTube

ok I tried to make several thing to make it revert mostly I revert the value(plus to minus, bigger than to lesser thant etc) so far with no luck here is my last attempt

Either nothing happen and the item remain on his last position or the itemp flicker from begin to end

Any idea how to solve that, I feel I am close to the solution