Assuming your duplicate entries are in column A and that entries begin on row
2, and that column B is an empty column you can use for this: Put this
formula into cell B3
=COUNTIF(A$2:A2,A3)
and fill the formula down the sheet. You will see numbers like 0, 1, or
greater. The rows with 0 are entries that are not duplicated above it. Any
non-zero number means the entry in A appears more than once.
Choose Data | Filter | Auto Filter
Then in the column with this formula (B in our example) click the little
pull-down arrow and choose Custom. Select 'greater than' for the condition,
and 0 for the value. Now only your rows containing duplicate data should be
displayed. Select all of the rows and use Edit | Delete | Entire Row
Turn off Auto-filtering and only your individual entries will be left.
You may want to make a copy of the sheet to practice this on so if something
goes awry (shouldn't) you'll still have the original data to start over with.