First step is to put a drop or two of a good penetrating fluid into the extractor plunger hole.
I recommend Kroil, which will creep into the hole. You can buy Kroil at many gun shops or machine supply shops, or online from Brownell's.
Stand the bolt upright and add the fluid, then allow to soak over night.
The plunger may pop up on it's own. If not, put the bolt face on a hard table top and tap it to jar the plunger out.
This will almost always get the plunger out. Then use a wire bent into a slight hook to pull the spring out.
Clean the tunnel thoroughly with solvent and pipe cleaners, or a small tube brush.
Just buy a new plunger and spring, and while you're at it you might buy a Wingmaster or Police milled extractor just on general principles to replace the MIM extractor you have.
New parts are sold by Brownell's and Midway.