If you take into account the time spent and the quality of the results of trying to straighten bent chain rings, you are probably better off just buying new rings. Also check the condition of the teeth: if they are badly worn, all you get for your effort is straight rings that have bad teeth.
Rings (and individual teeth, if necessary) can be straightened with an adjustable wrench. It's better done with the ring firmly attached to the crank, and the crank attached to the bike, so you can spin it and easily see where it is deviating from true.
You may be able to do the large ring, depending on how much room you have to grab it with the wrench (how much larger it is than the middle one).
The middle one will be impossible to do because the large one gets in the way. You have to remove the rings from the crank and then attach just the middle one to the crank. You will probably find that when the large ring isn't there, the bolts, which go through the crank and both rings, cannot tighten; you will need a couple of washers which have an inner diameter similar to the bolt holes to make up the missing thickness in place of the large ring.
The way the adjustable wrench is used is the obvious: just tighten it down, as firmly as you can, onto the area of the ring that you would like to bend back, and then apply leverage. Check for individual teeth being bent relative to adjacent teeth, and apply individual small bends to correct them. Teeth that are out of whack can cause nasty problems under load, like the chain riding up on the teeth and then snapping down, with each pedal revolution. It might be fine on a flat road, but as soon as you hit a hill: thunk, thunk, ...
I have experience trying to use a rubber mallet to straighten out a ring (off the bike of course). It wasn't entirely ineffective, but not very. Never tried a metal hammer; it seems like it could damage the teeth.
About special tools: if I do anything requiring removal of the rings, I remove the crank off the bottom bracket. That requires a crank puller tool. I'm not sure whether it's needed. If you can easily access the chain ring bolts without removing the crank, you're okay without the crank puller.