You are using Case Merge Premium and would like to implement automation as the result of a merge, such as performing a field update on the Parent (Master) Case.

The following fields are populated on Child Cases as the result of a merge, and can be used in the evaluation criteria for your automation.

• Status: The Merged Case Status you've defined on the Case Merge Premium setup wizard (usually, "Closed as Duplicate").
• Parent Case: Case Number of the Master Case chosen for the merge.
• Merged By: User who performed the merge.
• Merged Date/Time: Date/Time the merge occurred.

In order perform updates to the Parent Case, you will need to use Process Builder. For an example, see the following knowledge article.