A lot depends on how bad the tip set is.
It's possible to straighten a mild tip set just by applying a little pressure with your hands. I've also used the electric heating element of a stove, at a reasonable distance. You want to hold it maybe 1' above the coil and touch the heated cane every few seconds with bare hands, so you can feel it warming up. Stop short of it being too hot to touch. Use your common sense, be patient, bend it back in shape gradually.
If you scorch the varnish, you've done it wrong. If you see smoke, you've really done it wrong.
Sometimes it works permanently, other times the bend eventually comes back. There's no telling.
Ive also heard of people using steam. But that does tend to loosen the glue between the strips, and soften the varnish.
Common advice from cane freaks: if your tip gets a band from playing a big fish, switch it out with your spare tip. Or play the next fish with your rod upside down, so the tip bends in the opposite direction.
Weirdest thing about a bamboo fly rod with a tip set: as long as it's only a little bit warped, usually it still casts about the same. (The good ones cast pretty nice, imo.)