As I recall, it is basically:
- creating the noise profile with the whole audio selected
- Enter a reduction factor
- set the sensivity to -20
This reduces all frequencies 20 dB lower than the original audio by the set reduction.
It is actually a pity that the sensivity doesn’t allow even lower settings, e.g. to reduce audio under -35 dB.
However, the tool isn’t not intended for this purpose after all.