The tapping method doesn't always work, sad to say.
If it doesn't, do not use a screw driver to pry out the side plate: you'll probably leave dings in the steel, and it's possible to deform the side plate, with the result that it will never fit right again.
Add oil, and let it soak in a few minutes. Try tapping again. If that doesn't work, pry it out gently with a tongue depressor or Popsicle stick. Wood won't leave marks in steel, and if it's wide enough, there's a greatly reduced chance of deforming the side plate.
Replacing the side plate is usually easier. I make sure the edges are well oiled, press it in by hand with no more than moderate pressure, and use the screws to push it the rest of the way down. I've found it's better to half-tighten a screw, half-tighten the other, give the first a turn or two, give the second a turn or two, and generally ease the side plate back into place. If you tighten one screw all the way, you've just made it harder to tighten the second.