Complex sentence: Many research scholars have come up with theories regarding the origin of the Lepcha people, but the Lepcha people themselves firmly believe that they did not migrate to the current location from anywhere, and are indigenous to the region.
Split into simpler sentences: Many research scholars have come up with theories regarding the origin of the Lepcha people. But the Lepcha people themselves firmly believe that they did not migrate to the current location from anywhere and are indigenous to the region.