I congratulate you on your tenacity in pursuing the glitz look but have to give you a fail in the use of the search button above this thread.. however once again RetrouchPRO will come to your aid by entering the search phrase glossy lips into the box that pops up there you will find many helpful links..
just a few of which are: What's the best way to add gloss to lips? Lip Gloss - Photoshop Tutorial Face Makeover Retouching Different Parts of a Face
If you just want to enhance what is there ... on a New Blank layer... Paint the lips carefully with Black paint... Change the Mode to Overlay or Soft Light and adjust the Opacity to whatever you prefer
On another new, blank, Overlay or Soft Light layer (whichever shows the highlights best), paint in some specular highlights using a small soft white brush at a low flow following the natural lighting for the lips
Blur both of these layers as needed