I recently went through a similar exercise.....long story short my issue was not the rings themselves (though I took them off and did as above to check them for flatness), and not the spiders, but the crank arm itself had been slightly bent inwards and the pedal end twisted enough that I could feel it when riding. It took a lot of patience to set up a way of hold the centre part of the spider steady while exerting both a bending and twisting force on the other end of the arm to get it realigned. as dddd noted you have to be aware of what the metal wants to do (that said I am not "experienced" like some on this forum).

In the end I was successful but not without a bunch of cursing (mostly because the bolts holding the rings on were not coming off easily and I needed the rings out of the way to effect the repair on the arm).

Also to dddd 's point - I think I'd remove the small ring from the big one before trying anything and check them both for flatness.