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