Nvidia Hairworks, can't edit hair parameters ?

Hello everyone.
I’m new to this forum and to unreal in general. (and yes i know that beginning with hair shading is not the way to go, but i don’t really have a choice^^).
I have a problem, i follow this tutorial : HairWorks Quick start Unreal Engine 4 Pipeline - YouTube and also built unreal with the hairworks branch. Everything is fine at this point.
The hair also works, so no problem from this point. But i can’t edit the parameters. For examples in Physical parameters, i can’t change the mass Scale, Damping, or the wind direction etc, or in “Size” changing the density etc.
Anyone know why ? is this at least possible ? I really follow the tutorial step by step…

(Problem solved, i should have check the case overide)