This is a way of more comfortably getting rid of duplicates, by not having to go through them one by one. This feature is only available for Prospect and Opportunity plan and will appear automatically if switching from Lead plan to Prospect or Opportunity plan.
By going to Manage > Duplicates, you'll see the option for the report and a Dedupe option:
As usual, you first have to select 1 or more lists or none at all. By not selecting any lists, it will automatically include all lists. If you do click on the list bar, you'll get the options from the existing leads:
Next is the Dedupe Strategy:
There are three options and this is to decide what types of leads are going to be given priority when the automatic deduplication happens. The order of importance decrease as it goes from left to right.
The last option is the Dedupe Method:
This is to decide what will happen to the duplicates once found. If you'd like to know about the duplicate but not change anything, you can do a dry run and you'll get something like this:
You'll be able to see the priority, mode and the number or duplicates in each list.