For Studio 20, you can add VST plugins to the C:\Program Files...\Pinnacle\Studio 20\plugins\SystemAudio folder, and they will appear in the Audio Effects. Only drawback is that adjustment in the GUI has to be saved as a preset and then selected.

For Studio 23 VST is not possible, but there are so many standard FXs that is adequate for advanced editing.

Otherwise export the section as 'Audio Only' and use an audio editor for adjusting and put it back to the video project.
I like the Acon Digital products for this.

Using VST for other Studio versions you need to try it out.