Dressing the knot (tightening) is the process of using the knot itself as a 'standing' or anchored end [clumpy bit], and taking the 'running' or working ends [dangly bits] and running them 'through' the knot.
With the marlin spike / pokey object, tighten the Fist accordingly. I made two or three of these before I got it right. This is where getting the knot centered on your piece of paracord is important; there's less waste, as well. Be careful not to stab yourself with the pokey object. You will really get to understand the knot dynamics as you tighten it.