Update EXIF data (camera & lens)?

How can I update camera/lens information on photos through CC? I have scanned and shared images imported into CC that are missing this information and I'd like to manually add it.

I can edit the underlying files in my local library if that is possible using an external tool (I'm on Mac, iPad, iPhone), but I can't re-import all my photos that are missing EXIF data - there are too many. Surely there's a workflow for updating EXIF data in a photography tool like Lightroom?