The health inclusion rule can only be applied to the staleness, orphan, required and recommended metrics. Unfortunately, it cannot be applied to the duplicates metric.
As there is no way to create a health inclusion rule for a duplicate metric, a suggestion would be to create a table clean up job to remove records with discovery source as "duplicate for the target table.
1. Navigate to Automated Test Framework > Administration > Table Cleanup
2. Click on New
-Tablename = (select your table)
-Matchfield = sys_created_on
-Age in seconds = 1
-Active = true
-Cascade delete = false
-Conditions = Discovery source starts with duplicate
Once submitted, the duplicate records will be removed. Once this is done you can relax the setting by modifying the table cleanup to match field "last_updated_on" and configuring how often you'd like the table to be cleaned of duplicates via the seconds specified in the "Age in seconds" field.
Once the duplicate records are deleted, we recommend that you work on identifying the root cause and reducing the amount of duplicates being created.
You may also consider creating an enhancement request to our Product team to have the health inclusion rules apply to the duplicate metric in a future release. You can fill out a enhancement request via HI:
Self-Service > Enhancement Requests > Open an Enhancement Request