I believe you do it as follows:
Click File > Project Settings.
Ensure the General tab has focus.
Click the Advanced... button.
Click the LNG File tab.
Scroll the list to the [WebHelp] section.
Locate the item that reads: ContentCategoryList=Select a content category.
Click on it to select it.
Click the Edit button.
Change the text following the equals sign it to what you want it to read.
ContentCategoryList=Change this text
Press Enter to accept the change.
Click OK to dismiss the dialogs.
Generate and test!
Hope this helps... Rick