Sometimes there will be identical references in your library - two references for the same item. To get rid of the duplicates,
Open the “References” menu and choose “Find Duplicates.”
EndNote will show you the two duplicate records side by side, with any differences highlighted in blue. (The fields are editable as well.) You can scroll through the record and choose which one you would like to keep by clicking the “keep this record” button.
Don’t worry about accidentally deleting a reference. Deleted references are put into your EndNote “trash.” Until you empty your trash, any deleted reference can be recovered by dragging them back into your library.