I'm afraid you don't. You get a whole new snap in bulb - there are tons of them on eBay. Search for "chainsaw primer bulb". There are generally two kinds that are used on all sorts of saws, those with screw on mounting ears and those that clip in like yours.
Thanks Chris. I ordered some. I had some bulbs around from the little Honda tiller, and thought I might get lucky. Now that I know I can destroy it, I'll hit it with the heat gun and see if I can pry it apart.