I took a look at the files in the CS-80V directory and found where the global tuning value was stored. I installed the CS-80V demo on my other PC to find the default global tuning value.
Here is to set the global tuning back to its default value.
1. Load the file "C:\Program Files\Arturia\CS-80V\save\controlMidi" into a text editor.
2. Scroll to the bottom of the file.
3. Locate the entry for "TUNE_CS_80_TUNE"
4. Edit the value to be "0.500000" so that the line reads "TUNE_CS_80_TUNE 0.500000"
5. Save the file and restart the CS-80V.
Interestingly it would appear that the default value cannot be set using the global tuning knob inside the plugin. If you set the knob to 0.9993% or 0.9992% and check the value in the controlMidi file, then the value is either side of 0.500000 but never 0.500000 exactly.
Paul.