No worries at all – and sorry, I assumed you were using Logic based on the thread topic.
In FL Studio, the simplest approach is to insert Scaler Audio 3 (Audio FX) directly onto an audio track.
If you’d prefer to detect audio using the Instrument Plugin version of Scaler 3, there may be a way to route audio via sidechaining — similar to how it’s done in Ableton Live — however I’m not an FL user myself, so I can’t say for sure.
If you haven’t watched them already, I’d recommend checking out the Audio Detection Introduction and Plugin Types Overview videos. Cheers!