Have you already purchased this ticket? Afragola is really just a transfer station at this point, it's not a place where you would start or complete a journey.
There is a convoluted and out-of-the-way route by bus (two buses actually) that would take nearly two hours. Alternately you could take the Alibus to Napoli Centrale for 5 euro and a Frecce train from there to Napoli Afragola for 15 euro. The problem with this later plan is that there are only a couple of these trains per day so you'd likely sit around for hours waiting for one.