Follow Whites instructions on this (right now I can't remember their exact method).
I'm sure a rep will be by to give you instructions.
I've read a ton of different ways and suggestions from posters over the years, and this is what I do, and seems to work for me.
I wax the zipper while it's open. I lightly glide the wax down the zipper on both sides, and then again on the teeth on the inside of the suit as well. Because you cannot get to the first few teeth that are under the zipper pull when the suit is open, I close the zipper an inch and hit those few teeth, too.
I'm careful not to over wax the teeth. Too much wax can be a magnet for sand and other particles that can get between the teeth and cause damage.
I don't wax every dive. I wax every 2-3 dives.
Again, that's what I do, but you should follow Whites recommendations. Funny, these zippers are manufactured by the same company and installed in different dry suits, and the different dry suit companies using the same zipper sometimes have different waxing instructions.