Thank you for your post.
There are several parts to your post I don't fully understand.
Saving a Found Set of records is fairly simple. Suppose you want to find all postcodes that begin with "A". Pull down the View menu and select "Find Mode". Put your cursor in the postcode field and enter "A". Press return, and those records that have postcode starting with "A" are displayed. At this point, pull down the Records menu and select "Saved Finds -> Save Current Find..." You will then be prompted for a name. Once you enter a name, you can access it again at any time by pulling down the Records menu, selecting "Saved Finds ->" and selected the name you just gave.
To find duplicate records, go into Find Mode and enter an exclamation mark ( ! ) into the field that should be unique. This will then display every occurrence of duplicates. That is, the original and the multiples. You can then decide which record(s) you want to keep.
Please let me know if you need clarification for any of the above steps.