Check to see if the model already has a "wet" skin group. If it does, select it. If it doesn't, edit the model's VMT file.
The VMT file contains variables that the shader will use calculate the look of the texture. The section that determines the shineyness of a model should look something like this:
$phongexponent 5 // either/or
$phongexponenttexture [texture] // either/or
$phongfresnelranges "[0 0.5 1]"
Documentation on what each of these numbers do can be found here
and you can read how it works here