It's real easy. Have the Descendants of Siberian Immigrants, DSIs, (migrated across land bridge in the last ice age) produce authenticatable land surveys and deeds dated before 1492.
If their answer to that is, "We don't have those documents, things were done differently back then." then ask a follow-up question inquiring if they think the defense of things being done a given way in the past should stand as valid, or should we reject it and demand the documents anyway.
If they answer in the negative, then the documents remain required, and thus = no valid claim.
If they answer in the affirmative, then America simply states, "Well then, land acquisition in the past was also done by conquest." and thus = no valid claim.
They don't get to exempt themselves from civilized documentation then demand civilized behavior from a bunch of primitive explorers and conquerors.