Final answer:
To update existing target table records when importing data from an import set, a transform map is used with properly configured coalesce fields to match and update records.
Step-by-step explanation:
When importing data from an import set into a target table, the option that allows you to update existing records is to use a transform map. Transform maps in ServiceNow or similar platforms determine how fields in an import set map to fields in an existing table. If a matching record is found based on the transform map's coalesce field, that record will be updated with the imported data.
To ensure an update rather than an insert, you need to correctly configure the coalesce field. This field tells the system how to find a match between an import set row and an existing record in the target table. If the field values match, the record is updated; if there is no match, a new record is created, assuming the transform map is configured to allow inserts.