The magic word is “de-esser”
There are two specific de-esser plug-ins for Audacity …
Steve’s … https://forum.audacityteam.org/t/please-help-with-de-sser/48588/14
Paul-L’s … https://forum.audacityteam.org/t/updated-de-clicker-and-new-de-esser-for-speech/34283/1