Delete duplicate photos in icloud online

I have backed up my photos on icloud and don't have a local copy of all of the photos in "photos" app on my mac. I have duplicates of many, but not all of the photos when I view them in icloud. How do I delete the duplicates without going one by one and deleting the dupes? Also, I have read that 3rd party apps are not recommended due to potential corruption issues, but is this truly a risk?

(NOTE: I have researched this extensively but have never seen a solution offered that addresses the duplicates in icloud.com online. Many of the answers I have seen address deleting duplicates of photos in the "photos" app on a Mac and involve downloading photos to an external hard drive, which I don't have. In this case I am trying to delete them from the online icloud.com.)

Looking forward to your advice.