when I click on Enhance, then replace color shows up, then I click on "replace color" I get this response

What version of photoshop and operating system are you using?

Actually i get the same message when in pse 15 on mac osSierra i click on Learn More About Replace Color.

Probably something wrong on the adobe side.

The link should actually be:

https://helpx.adobe.com/photoshop-elements/using/adjusting-color-saturation-hue-vibrance.html