Audacity can take a video apart, but not put it back together. Export a corrected audio track from audacity and replace it with your video editor. Audacity won’t save a sound file. You have to export one. Start with WAV (Microsoft) 16-bit and try exporting MP3 if that fails.
So for me, with Windows 10, in Audacity, I click on Tools > Nyquist Plug-in Installer, then locate the downloaded LevelSpeech2.NY file and click OK. Then I select Tools > Add / Remove Plug-ins, select “New” in the upper right-hand corner, locate LevelSpeech2 and select Enable, then OK.
To use the plug-in, I select some audio (Ctrl-A, for all), then Effects > LevelSpeech2 (LevelSpeech2 is below the line in the Effects Menu).