HOW DO I CLEAR THE CUSTOM PREVIEW AREA?

Are you referring to this?



If that's it and you only wanted to revert to the default preview string, delete the text that you entered in the preview text box (A) and click on the Submit button. However, if you made other customization to the font preview and wanted to revert everything to the default, click on the Reinitialize (B) link found right above the Submit button.