According to YEC, how and when did the Americas become populated?

I’m aware that modern scientific theories propose an ice bridge which allowed for travelers to reach the Americas and that this fact accounts for the existence of Native Americans (and South American tribes, etc.). However, it would seem to be problematic on YEC to propose a similar idea given that the ice bridge is dated much earlier than 6000 or 4200 years ago (4200 being when answers in genesis dates the Tower of Babel). So what is the explanation for the human population in America, especially at the scale which it was presumably at?