Upon installation Duplicate Check was installed for the Lead, Contact and Account Object by default. Perhaps you added additional Objects during install as well. 

After installation, you can manually add and configure more Objects to Duplicate Check via DC Setup, but you can also choose to add Objects via Plauti Cloud:

1. Log into Plauti Cloud
2. At left, go to Installer > Install Applications  
3. At Select a Connection, select the Org where PDM and Duplicate Check are installed
4. At the Duplicate Check line, click Configure
5. At Search and Select More Objects, add the Objects you want to add to Duplicate Check
6. Click Next
7. Review the configuration summary and click Start. 
   The selected objects will now be added to Duplicate Check. 
8. Keep track of the configuration progress via Install Applications > Show Progress, and once configuration is finished, you can check the result via Install History.
9. Once installed, go to the Duplicate Check app > tab DC Setup. Select the newly added object at left and configure it further.