We can´t know precisely how and why the first inhabitant of America arrived. Through genomes and archeological studies, the scientists have made two principal hypothesis.
The theory of late settlement: the Paleoamericans entered the continent during the last ice age when the passage to the New World was possible through the Bering Strait (between 15,000 and 14,000 years ago a. C.)
The theory of early settlement: humans arrived much earlier. The genetic information is added, that it connects us with populations of the northeast or the east of Asia.
There is also a theory that states that South America was populated by a migratory wave that came from Oceania. Why is this information uncertain? Because of the temporary distance.