Wrangle Duplicates Using Duplicate Record Sets in Lightning Experience

You can now use duplicate record sets in Lightning Experience. When the Report option is selected in a duplicate rule, Duplicate Management creates duplicate record sets of duplicates found by the rule. You can also create duplicate record sets, adding any records you like as duplicate record items. In Lightning Experience only, you can even use duplicate record sets to merge items on the same object.
Available in: Professional, Enterprise, Performance, and Unlimited, and Developer Editions

User Permissions Needed
To view duplicate record items: View on accounts, contacts, or leads
To merge duplicate record items (Lightning Experience only): Edit and Delete on accounts, contacts, or leads
  1. Open the App Launcher and find Duplicate Record Sets.A duplicate record set in Lightning Experience, with Compare and Merge action
  2. Create a record set, add records to an existing set, or delete a set. Or compare the records in a set and merge them.Several potential duplicate leads, with checkboxes to select up to 3 records to merge