Adding an App Icon Set or Launch Image Set
Organize versions of your app icons and launch images in image sets, which you can add to an asset catalog.
In the project navigator, select an asset catalog.
Choose Editor > New App Icon.
An empty app icon set is created, with an image well for each image representation in the set.
In the Finder, select an app icon and drag it to to the appropriate image well in the set viewer.
Alternatively, you can add app icons by choosing Editor > Import.