NO! Don't use the straightening iron. Not as a first step. It's a valid approach, but is somewhat further down the list.

First, just use heat. Blow dryer. Do a blowout to straighten the hair...basically you brush it straight while applying heat. This has the benefit of being as safe and non-damaging as anything you're likely to try, and it's easily and quickly done when needed. Youtube "blowout" and you'll see the technique used, usually on women's long hair, but the principle is the same.

If that isn't enough, you can add some product like a hair gel, or even use the oils in concert with the heat. This will usually relax the curl.

Then, and only if you need more straightening, do you bring in power tools.

The idea is to cause as little damage to the hairs themselves as is possible.