Lola W. better late than ever so... she is next to kimi (kim minji, the girl with blonde short hair and bow at the very left back) you can spot her when they do the left arm up, right arm up and center both arms up dance brake, she is at the left back going the both arms up at 2:27 (there is a guy in Blue sweater between kimi and sohye). i hope this help and sorry for the long answer.
Mario Guimarães so... i know this was posted a year ago, but just in case you still want to know: Chungha wasn't in this performance because she was injured at the time (a leg i think).