Complex sentence: The song was released on July 31,2014 as a 5-member group, GyuHee & Bichen that left the group, replaced by new member, Jung Yoon & Seoyeon being inactive for this comeback promotion activities due to health issues.
Split into simpler sentences: The song was released on July 31,2014 as a 5-member group, when GyuHee & Bichen left the group and were replaced by new member, Jung Yoon. Seoyeon became inactive for this comeback promotion activities due to health issues.