One way is to do a select distinct on the table, zap it, then do an append from the select result.

select distinct * from table into cursor cursa
if !used('table')
    use table excl
    zap
    append from dbf('cursa')
else
    use in table
    use table excl
    zap
    append from dbf('cursa')
endif
use in table
use in cursa

Now you have a table with no duplicate records. The next thing is arranging the app to not allow duplicates to be created.