Hi there,
All emails are fully customizable via our settings panel, or in the Email tab of your Form edit screen. Here’s docs on that:
https://givewp.com/documentation/core/settings/emails/new-donation-notification-email/
Currently though, in order to customize the header (it says “New Donation!” on your screenshot) you need to use this custom snippet:
https://github.com/WordImpress/Give-Snippet-Library/blob/master/email-customization/custom-email-headings.php
If you need guidance implementing custom PHP functions on your website, we have this guide here: https://givewp.com/documentation/resources/adding-custom-functions-to-your-wordpress-website/
Thanks!