Prepare an icon with a size of 128x128 in tga format, and place it in the Complete folder. After that, open the map in the editor, select the hero, and in the properties, check the "Custom Icon" box, then choose the icon from the Complete folder.
And I've already tried the same method for the splash screen image, and it works.
Added 2 minutes later
By the way, if someone downloads the map, will they have to manually insert these images?