You can define your own logo image from within the ePanel theme options page in your WordPress Dashboard. To locate ePanel, click the Appearances > Divi Theme Options link in your WordPress Dashboard. Within ePanel, under the General Settings > General tab, locate the "Logo" field. In the field, input the full URL to your logo image. You can use the "Upload Image" button below the field to upload your logo image if haven't already done so. After uploading, copy and paste the URL to the file into the field and click "Save" to save your ePanel settings.
If you don't already have a logo image, then you can use the included logo.psd file as a starting point. If you have Photoshop, this file can be opened and the logo's text can be easily edited using Photoshop's type tool. If you don't have Photoshop, then you can use included logo_blank.png file as a blank canvas in a different graphic design program. These files (logo.psd and logo_blank.png) are located within the Theme Package inside the /psd/ folder.