There are (at least) two kinds of wheel problems, lateral and radial. Side-to-side wobble is the kind of thing that you should be able to take out by tightening spokes. But 'hop', where the rim moves 'up&down' rather than 'side-to-side' when you spin it, if you increase spoke tension you can only pull it in further, if you loosen spoke tension you probably won't make much difference.

Only thing I've heard for that is try to locate the center of the hop, where the rim is most bent inwards, and try to bend it out.

Put two 2x4s on the ground, spaced maybe 6-8 inches apart. Stand the rim on the gap between the 2x4s so the center of the hop is straight down, and the wheel does not touch the ground. Put your foot into the rim and add body weight to try to push the rim back out a little bit. Or probably since a foot is too wide, put another 2x4 through the spokes there, and try to push down on both sides to bend the rim back out.

If you want to be really careful, get the spacing of the original 2x4s just right so that the rim doesn't touch the ground at first because of where it is bent in, but if it were perfect, it would touch the ground. That way you can't bend it too far.