Use the original list and then compare them with a simple is formula
appended to the original list, so if the original list is in A2:A500, then
insert temporarily a blank B column or use the one that exists if it is
empty, assume the list w/o duplicates are in Sheet2!A2:A480
=COUNTIF(Sheet2!$A$2:$A$480,A2)>1
copy down the formula, then apply data>filter>autofilter (make sure you have
headers) and filter on B for TRUE, then just copy the filtered list
somewhere else, that is the list with duplicates