Ok, there are a few different ways you could go here.
#1 starting with the juice you already have - say you have 30ml of 6ngml nicotine content. Simply adding 30ml of your choice of 100VG or 100PG or whatever mix of them you wish and presto - you have 60ml of 3ngml nicotine.
#2 Assuming that you ended up with more than ONE pod, you can make up/mix whatever VG/PG you wish and fill that POD with it. Zero ngml nicotine content! (simple!)
#3 Personally I get flavors from "Bull City" and use syringes to measure. I generally mix into a 30ml bottle. Funny thing is that MANY of their flavors only require ONE ML flavoring per 30ML bottle to taste good! (sometimes less other times more - you get the idea!)
Last but not least, coils/pods last longer without flavors. If you wish to just have the in/exhale + hand/mouth the simple unflavored nicotine free might be the way to go.
g.