A group of people from the North-East of India claimed to be the descendants of the lost tribe of Menashe. It was confirmed in 2005 by Rabbi Shlomo Amar Shlit"a, the then Sefardic chief Rabbi of Israel. They still go through a process of conversion for about 2-3 months (see here).
What is the halakha for lost tribes? Do they need to do "Tikkun haMiddot"?