- Navigate to the Salesforce Setup - Administration - Users - Profiles
- Find your Profile and open the profile setup by clicking on your profiles name.
- Click "Assigned Apps".
- Click "Edit".
- Find "Duplicate Check (dupcheck__dc3App_Lightning)" in the list, and make sure the checkbox is set to "Visible".
- Click Save.
That's it. You are now able to access the Duplicate Check application via the App Launcher again.