Definitely seconds. You can also get a feel for it by it sitting a bit over the steam from boiling water too. Obviously that would take a bit longer like 30 seconds to a minute. Use oven mitts or towels. It will get soft and easier to bend. Once you get the right shape, hold it in place while letting it cool down in front of a fan or something.
I would leave helmet alone unless it bugs you. If so, try taking it apart to do just back piece.
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