Complex sentence: Pham-Kho-Sowai (a harvesting festival) is a popular festival of the Bugun people which is now celebrated on a fixed date i.e., 10 September every year.
Split into simpler sentences: Pham-Kho-Sowai (a harvesting festival) is a popular festival of the Bugun people. It is now celebrated on a fixed date, starting on 10 September every year.