I’m not sure immigration is the full answer. It may help. But, there is a very good reason why Koreans (and many other developed countries) have diminishing populations. The cost of living is out of control. Immigrants just can’t move to Korea and start families. Unless they target (i.e. exploit) people from poorer countries who will accept a substandard quality of life and work themselves to death by scraping by to provide for a family.