How do we change our update statment? we want to add rows from NEWschoolmark table th

How do we change our update statment? we want to add rows from NEWschoolmark table that does not existed in schoolmark table
UPDATE schoolmark INNER JOIN NEWschoolmark ON schoolmark.field1 = NEWschoolmark.field1 SET schoolmark.field3 = [NEWschoolmark].field3;