Move a component in assembly

Ok, I created an assembly and inserted a new part in the assembly then make it float. The part just has a name but no geometry. I then edit the new part to work on it and created geometry by using converted entities. Now I want to reposition the part using mate but when I update the assembly the part goes back to its original position where it was modelled. How can I fix this? The part still shows under defined (-) next to its name.

SolidworksAssemblies