my total Libraray is 15,475 and its duplicate items are 8,260. After removing duplicates, remaining items should be 7,215 but instead of this, there are 10,827 papers in my library now, which means difference of 3,612 papers are still there in my library that needs to be removed from library but now when i click on duplicate items, its empty.

Any guidance regarding how to identify those remaining 3,612 paper and remove them?

If you have 8260 Duplicate items, then removing them would only decrease the library size by 4130, which seems to be at least close to where you are. If some where triples or quadruplets, that'd explain the remaining difference.