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I am sorry if I do not understand you.

I think, what you are asking is: How to Delete one or more photos from a Smart Album or Album in Photo app?

If this is your issue, I think I can help solve it.

1. Select the photo or group of photos that you wish to delete
2. On your keyboard, press all three keys simultaneously: command, option, delete
3. This will move all those selected photos into Trash. From there you can permanently delete.

Deleting Photos from a Photos Library

1 - regardless of where you are in the library, i.e. Photos, Memories, Favorites, People, Recents, Imports, albums or smart albums, select the photo(s) you want to delete and use the key combination of Command+Delete to move the photos to the Recently Deleted smart album.    Without the Command key held down you'll be presented with a confirmation Yes/No window regarding the deletion. 

2 - click on the Recently Deleted smart albums in the sidebar.

NOTE 1: If you're using Photos 1.2 or earlier use the File  ➙ Show Recently Deleted menu option.

3 - in the Recently Deleted album you can opt to let the photo automatically delete after the 30 day waiting period is up, delete them immediately or restore them to the library.

NOTE 2: deleting a photo from an album, slideshow, book, etc., with the Delete key only deletes the photo from that item. There is no key combination that will delete a photo from a project and move it directly to the Recently Deleted smart album.

NOTE 3: deleting a photo from a Moment or Collection (the Photos window) or the All Photos window deletes ALL occurences of that photo in the library.