The Unique Import feature can be enabled in the *Object* Settings.
Duplicate Check Unique Import feature does not have its own import tool but it works with any tool available for Salesforce (Salesforce Data Import Wizard, Dataloader.io).
Make sure to apply a scenario to Unique Import feature. Otherwise, it won't work.
After an import, a job will start automatically at the DC Job page.
Duplicate Check will trigger itself only after an import of 2 or more records. These records must be imported as 'new records' and not as an 'update' to any existing records.
If the job gets aborted or does not complete, then a 'unique import' button will appear. After clicking the button, the Unique Import job will continue.