This feature will only appear in Record View if you Administrator has enabled the Merge Party and Copy Party roles. It will let you copy information from one party to another (Copy); as well as merging two parties into a single party (Merge). .
To start Copy or Merge, click on the Copy/Merge option in the Record Toolbar when you open a case. This option appears only when there are two or more parties associated with the record.
Then, select your Source Party: the party you want to copy information from; and then your Destination Party: the party receiving the information:
Keep in mind that there is no undo for Copy/Merge. Copy permanently overwrites data. Merge permanently deletes source party information.