My Photo Sharing extension plans to use the same design assets (for navigation and for adding \'stamps / stickers\' to the photo).
As explained in App Sa
here the steps to resolve your issue:
go to xcode open your app which contains the app extension feature
go to target in your xcode project and select your app extension name
go to build phases
expand the copy bundle resources then click "+" button and add the image assets folder from the finder.