Sorry, third party plugins e.g. … Soften the S - #2 by Trebor [ de-essers can also be used to re-ess ]
As I mentioned above I don’t think a re-esser is going to cure an intermittent lisp as it will boost all sibilance indiscriminately.
What I was suggesting in my previous post was to individually boost each lisping ess using treble-boost equalization so its spectrogram looked more like the clear “s” of the word “several”.