To get app extensions you have to purchase applications, that include photo editing extensions.
Most of these apps are expensive.
The one exception I found was BeFunky Express. When I downloaded it from the AppStore, it was free. Check this out, if it is still free I don't see a price at the App Store, because I already own it. BeFunky is fun. It includes a touch ups for portraits - skin smoothing, teeth whiten, eye brighten, and a HDR adjustment.
Th other extensions are also nice, but you have to pay for them: Affinity Retouching works great, Intensify has great presets, noiseless is easy to use and lets you compare the original and the adjusted side-by-side. Snap heal combines different image enhancements in one tool.
