You will need a pair of pliers, ink refill and your Stampin' Write Marker.
Remove marker cap from one end. Using the pliers, carefully place them on one end of the colored portion of your marker, get a really good grip and pull straight out. You will have to use a little bit of muscle but this will not damage the plastic end at all. Flip the opened end facing down and the inked reservoir tube should fall out. It looks like a straw.
Using your ink refill, add drops to each end of the ink reservoir tube. Replace marker parts back where they belong and make sure you push the colored plastic end with your pliers until you hear a "click".
TIP: Always store markers laying flat so that the ink does not end up all at one end!