The settings I posted are for sound normalized to 0dB , the submitted sound was quieter : normalized to about -10dB, so in that case threshold on the DeEsser should be lowered by 10dB to -40dB , (rather than -30dB shown) , i.e. some trial&error experimentation with the threshold is required , ( in +/-1dB steps), to optimize , as it depends on the volume , however I think the other settings shown have been optimised.
The settings shown are to correct the whistle which occurs on some plosives like “T” & “D” , which is the most conspicuous problem. Another application of the DeEsser with different settings will be necessary to address any excessive sibilance above 7kHz.
One can get a copy of Paul-L’s DeEsser & DeClicker plugins here … Updated De-Clicker and new De-esser for speech , they are attached to the bottom of that post by Paul-L.
Here’s a link on how to install those plugins into Audacity … Audacity Manual