If you can’t find a search to automatically grab them all, I think you’d have to deal with them one at a time as you come across them.
If you want to delete them, use PhotoStructure | How to archive, remove, and delete photos and videos in your PhotoStructure library
If you want to keep them but handle them differently, add a keyword tag. You can do that with external software or wait for PS to implement it. Support editing asset keywords
Once these files are tagged, you can completely exclude them from PS with the keyword blacklist Excluding media with specific tags, or once users are implemented you could (hopefully) exclude the keyword only for certain users When users exist...assigning tags to users