Icons gone and can't figure out where they went.

Are you saying they disappeared off the dock or desktop? If they did, you can drag them to the dock or desktop from the Applications folder in Finder.

If they disappeared out of the Applications folder you need to reinstall them. If they are Apple apps that brings up additional questions as most can't be uninstalled.

You don't generally look for apps in Settings. Settings is a feature of a app that allows customizations.

My guess is you need to reinstall the two apps.

What app, if any, are you talking about?

On the Mac, there is no special App for Facebook or amazon, so you will not likely find those in /Applications.

those could be web links, copies of a web page saved to your desktop.