Get out the Bag of Gears and glue some onto the knobs on the side with two-step epoxy or superglue. What’s more steampunk than a gear that serves no apparent purpose?
Now it’s time to tackle the straps and bridge. The goggles came with an elastic strap and plastic covered metal chain bridge. That’s not terribly Victorian. I’ve got a bag of scrap leather, though you could use faux leather, canvas, or other fabric for this. I started by cutting a thick rectangle slightly larger than the existing bridge piece and notching it on either side.
Next, I flipped the leather over, rough side up, and tacked the center down using Fabri-Tac. The end result should look something like a sideways letter I.