Is there a way to "fix" my stainless steel fry pan that does not sit flush on my cooktop stove?
I have had some limited success using a technique borrowed from large steel fabrication and construction, specifically ship building. In order to 'flatten out' the steel wall and deck plates on a ship, after they are welded into place, they are alternately heated and quenched with water, which has the effect of shrinking the metal, reducing or removing the warps created from the heat of the welding process.
What I will do with a warped pot or pan is heat it dull red on the stove and apply wet cloths to the warped part(s), if the whole thing is warped, I start in the middle. Successive treatments do reduce the warping. Just be careful, and wear leather gloves and a heavy long sleeved shirt, the steam is hot, and will burn you very badly if not careful.
No, there isn't. You'll either have to live with it, or get a new pan.
Some pan materials are more resistant to warping, like cast iron (either enameled or raw). Those are a little pricey, but if you take good care of them, your grandkids will still be using them.
Cook something in the pan, even if it's just boiling a little water. Take it off the stove, dump out the contents, but do NOT cool it or run it under any water.
Now, flip it over face-down on a large, flat surface. I have had good success just using a dishtowel over a plastic cutting board. (Don't use a wooden cutting board, as what we are about to do in the next step could break it apart at the joints) You want the rim of the pan face-down in good contact with the level surface all the way around, with the handle hanging off the table where it won't interfere. Very important.
The idea is to have that rim face-down, the pan still HOT (hence the dishtowel over the plastic cutting board, so it doesn't melt). And this needs to be on a STURDY table. You'll see why.
Take a large rubber mallet (NOT a regular steel hammer!), and whack the center
of the pan a few times. Don't be shy. Hit it hard.
Just a few whacks, test it. If it's not enough, flip it and whack it again.
NOW... From now on, after you cook in it, do NOT put it anywhere near any water or anything cool until it has a chance to cool on its own. If you dump out the contents and immediately put it under water, even warm water, the rapid temperature change will make the bottom warp upward.
It is true that really high-quality cookware with very thick bottoms does not suffer from this. But your average everyday stuff, you can still avoid the problem if you avoid rapid temperature changes.