To restore the default view, try the button in the bottom-left corner of the window... 
To restore everything, Ai offers these suggestions...
Start by uninstalling WavePad from your computer. This will remove the program but not necessarily reset all settings.
After uninstalling, you need to manually delete the configuration folders. Look for folders named "WavePad" and "Components" in the following locations:
Typically found in C:\Users\YourUsername\AppData\Roaming\NCH Software\WavePad and possibly other related directories. You might find these in ~/Library/Application Support/NCH Software/WavePad.
Once you have deleted these folders, reinstall WavePad. This should restore the program to its default settings.
Alternatively, if you are looking for a simpler method to reset specific settings within WavePad without uninstalling, you can try using the "Reset" button available in some options, such as resetting the file naming format or auto-numbering settings1. However, this method may not reset all settings globally.
There's also the Revo free uninstaller method. Scan and delete all registry entries that it lists. Then reinstall WP.