When I got to the point of using the XCode (version 9.3) application loader, I get the error:
ERROR ITMS-90022: "Missing required icon file. The bundle does not contain an app icon for iPhone / iPod Touch of exactly '120x120' pixels, in .png format for iOS versions >= 7.0."
but I don't know where to upload a 120x120 app icon - as the only one that I uploaded at iTunes was 1024 x 1024, and the app is supposed to convert these by itself to the various sizes.
Supposedly this is an XCode issue. I am using XCode 9.3