Improving a (faint) recording of a talk from original

Try the famous Paul’s de-esser Nyquist plugin:

https://forum.audacityteam.org/t/updated-de-clicker-and-new-de-esser-for-speech/34283/1

The download is in the first post of that thread.

How to install Nyquist plugins:

http://wiki.audacityteam.org/wiki/Download_Nyquist_Plug-ins