Select Use Asset Catalog (I opted for just doing it for the App Icons and not the Launch Images because my No image found errors were all related to App Icons, as yours seem to be), then drag and drop the appropriate icons into their correct spots.
The first time I did this it was a bit messed up, I believe because I had set the resources, so I ended up selecting "Don't use asset catalogs" which reset the resources to be blank, deleted the asset catalog, and then selected Use Asset Catalog again.
At this point all the spots were blank and I was able to drag and drop the correct assets to the correct places. Note that there is no 1x 60pt iOS 7 icon slot.
I found this other related thread which had the answer: How do you update the app icons and launch images to support IOS 6 and 7 simultaneously?