You can't. A Zip code is a polygon by definition, not a co-ordinate. It does not make sense to generate routes to Zips because they are polygons. Can you step back and tell us the problem you are trying to solve? What you are doing does not make sense to me.
Take a look at our sample in the Web control that shows 5 US Zip Codes and you will see what I mean https://samples.bingmapsportal.com/?search=zip&sample=load-multiple-boundaries-geodata