All my hoops already have tape on them, will this melt the tape and make it not stick? Also thanks!
Yes, the blowdryer would probably melt the sticky side of the tape--not good for your hoop.
This summer I would just lay mine in the sun and it would correct them. But I've heard a bathtub full of hot water will work too.
I usually just bend mine into shape by hand, no heat necessary. If you work it for a little while, it'll usually get into shape, no problem. Just put it against a wood or tile floor or wall to make sure it's nice and straight.
If you can't manage that, heat is your only choice. Try to isolate where you want to bend it and use a hair dryer only on that part. Gaffer's tape can stand up to damage a lot better than you think. Just don't leave the heat on it for very long. It only takes a minute or so to make the hoop a wee bit more pliable...the gaffer's tape will take longer than that to melt.
As the weather gets colder and you can't put the hoops out in the sun to warm up, a wood stove (or even propane or something like that) is the next best thing. If you put the hoop near the stove for a little while, try 5-10 minutes to start, the tubing will warm up enough to work it into a circle. I have done this before when my hoops are a little out of whack. It works great, just make sure you don't put the hoop too close to the stove, of course.