Ouch! That’s not meant to happen (and I realise that’s cold comfort for you at this moment).
The settings might not be lost. If you still have the .msi from the previous version, uninstall the version you’ve just installed, then re-install the old one. With the settings now visible, back them up (File / Export) and repeat the upgrade. If they’re not there after this second upgrade you can restore the backup from File / Import.
If you no longer have the old .msi, you might be able to locate and hand-edit the original settings back into a CSV file to import. Check if the old config is still here:
If it’s not here, try the \AppData\Roaming\ folder tree.
(You might need to go to Explorer and enable View / Hidden Items before you can see the “AppData” folder).