If you're talking about the little nylon sleeve, call Hi Point and tell them you need to upgrade your firing pin assembly as they aren't used anymore, the new design has a little fat short spring that goes around the longer, skinny main firing pin spring, the two sleeves aren't used. Might want to replace the extractor and it's spring as well, since those have been changed as well since your pistol was manufactured it seems.
Well I have two springs but on the diagram that came with my C9 it says that there is a sleeve of some kind that separates the two springs. Either way I am going to call Hi Point I think cause there has to be something that goes there. The darn springs will just go inside one another and it wont work that way