Products for curly hair are designed to minimize the negative effects of curls (such as frizzyness) while attempting to accentuate the curl.

I don’t think I’ve ever seen a product for straight hair other than maybe a straightening iron (and mists, etc. designed to be used before/after ironing), which does indeed iron your hair in an attempt to make it straighter.

There are two exceptions to this: a permanent (“perm”) solution does actually make your hair more curly. Despite being called permanent, it only lasts a few weeks or months. The opposite of this is called a hair relaxer. It’ll make your hair more straight for a similar amount of time. Both of these are more harsh chemicals, and people generally go to a salon to get them done professionally. There are also home versions sold.

In summary, read the entire package before you use it on your hair.