When mosiach comes it says everybody in the whole world will believe in Hashem (Zecharya 8:23):
כֹּה אָמַר ה' צְבָאוֹת בַּיָּמִים הָהֵמָּה אֲשֶׁר יַחֲזִיקוּ עֲשָׂרָה אֲנָשִׁים מִכֹּל לְשֹׁנוֹת הַגּוֹיִם וְהֶחֱזִיקוּ בִּכְנַף אִישׁ יְהוּדִי לֵאמֹר נֵלְכָה עִמָּכֶם כִּי שָׁמַעְנוּ אֱלֹהִים עִמָּכֶם
Thus saith the LORD of hosts: In those days it shall come to pass, that ten men shall take hold, out of all the languages of the nations, shall even take hold of the skirt of him that is a Jew, saying: We will go with you, for we have heard that God is with you.'
But what about the uncontacted tribes, for examples in the Amazon rainforest, Papua New Guinea? How will they find out about Hashem, since they aren't known to the rest of mankind -- they didn't have any prior contact with Jews, so they couldn't have found out through them, as the above verse claims.