To change the heading of your Zylpha generated index, first navigate to the index and pagination settings by clicking the "Index and Pagination" row on the bundle building page.
This will reveal a side panel on the right containing the index and pagination options. Under the "Index" section you can amend the index heading by clicking the "Heading" field.
If you've already generated your bundle before changing these settings, please regenerate your bundle again for the changes to take effect.