Put the hammer away !!!

There are 3 ways to fix flatspots

1) In mild cases, you loosen the spokes at the flat spot, and tighten the spokes before and after the flatspot. Tightening them pulls in the rim on either side, and forces the flat spot back out to compensate. Then you can retighten the spokes at the flatspot, but they may have to stay a bit looser than the others.

2) For worse flatspots, you can use a rim puller. you loosen the spokes again, and the rim puller rests on the rim, with a hook on the inner side of the wheel and a huge screw to pull the rim out. This tool probably costs more than the rim, but a friendly shop might let you borrow theirs.

3) Put on a new rim. Sometimes easier than fixing the old one. Tape the new rim to the old rim, lining it up correctly. Undo each spoke & transfer it to the new rim. Tighten & true it up.