First of all, you don't have access to powerups immediately. They only begin to unlock after you play songs, I remember it being at least a couple before Cleanse became available.
Next, this trophy requires you to repair your combo using either Cleanse or Flow. You'll need to hit specially shaped notes (green for Cleanse or Blue for Flow) in sequence and you'll hear a voice saying "Cleanse" or "Flow". To deploy you then press the X Button.
Now here's the tricky part. You first need to build your streak up to 4x by clearing four charts. Then, once you have a 4x on the right side of your screen, miss a note and you'll notice the streak breaks. But if you press X IMMEDIATELY after with Cleanse or Flow, you then either clear the track with the former or enter flow mode (like your flying around the screen) and this trophy will pop. This can be done on any difficulty and any song.