The Preheader Section is currently a placeholder and doesn't add functionality to the New Email Editor.
If you'd like to see the Preheader Section functionality enabled in the New Email Editor reach out to your CSM to submit Product Feedback. Product Feedback will inquire with the development team if this feature can be added to the development roadmap.
If further assistance is required, submit a ticket to Punchh Support. (For help submitting a ticket, click here)