Unless the blade is really out of square, I'd use the lateral adjustment, and just let it be canted a bit.
Otherwise, you'll need to regrind the blade to square, then cut new teeth in it. It's not a hard job to do that, but does require some meticulous attention paid it.
A three-cornered file will work well, but an even better choice would be a 'feather-edge' file like those sold for sharpening Japanese pull saws. It's probably going to take a couple hours to do it right. Sharpen the blade, same as with a conventional iron, then (being VERY CAREFUL not to cut yourself) cut in the new teeth. Wear gloves (preferably Kevlar) and keep bandaids handy.