This method is defined in the generated resultset code.
public void ResetToUnmodifiedExisting()
A record is created, filled with values, reset to not modified and the status is set to DataRecordStatus.Existing:
customers.ID = 100;
customers.Firstname = "John";
customers.Lastname = "Smith";
When Recordset.SaveChanges() is called, nothing will happen for that record as there are no modified columns.