The hot+cold recipe:
FIRST, use a hairdryer on high to heat the arm; keep the nozzle at least 6-7 inches away. Heat for a minute or two -- until you feel its hot. Be careful here, keep your eye on the arm, don't just walk away and leave the dryer blowing on it. The arm will melt eventually.
SECOND, drop arm into very hot water in your sink. No need to boil, just let the faucet run until the water is piping hot. Let the arms sit in there another minute or two.
THIRD, wipe arm dry and quickly pop it into the freezer. Another couple minutes, then remove and roll in your hand just to warm it up a bit. That's it. This hot+cold process worked for me to get it back to its original shape and maybe even shrink it down a tad.
You may want to measure the arm before, or mark down its length on a piece of paper, then when you're done you can check your marks and see that it has in fact shrunk down a bit.