N/task Module
EntityDeduplicationTask.masterRecordId
Property Description: When you merge duplicate records, you can delete all duplicates for a record or merge information from the duplicate records into the master record. Use this property to set the ID of the master record that you want to use as the master record in the merge. You must also select SELECT_BY_ID for the EntityDeduplicationTask.masterSelectionMode property, or NetSuite ignores this setting.
Type: number
Supported Script Types: Server scripts For more information, see SuiteScript 2.0 Script Types.
Module: N/task Module
Since: 2015.2
Search NetSuite - https://system.netsuite.com/app/help/helpcenter.nl?search=EntityDeduplicationTask.masterRecordId

// Code Example 1

//Add additional code

//...

dedupeTask.masterSelectionMode = task.MasterSelectionMode.SELECT_BY_ID;

dedupeTask.masterRecordId = 107;

//...

//Add additional code



//SOURCE: https://system.netsuite.com/app/help/helpcenter.nl?fid=section_456971679686.html