This wasn't included in the previous Dream Concert posts. They performed at the very beginning of DC and they weren't a part of the main artist list since they haven't debuted yet, obv. They performed their OST track "Give Me" for the k-drama Prosecutor Princess. You can also hear that they just finished doing a PCD - Buttons cover.
cr: Sweetz15 @ YouTube and An9elicMelody (international Muses forum) 1, 2