Like any other themes, Divi has a default footer credits that goes like this: “Designed by Elegant Themes Powered by WordPress”
Before Divi version 3.0 it was very hard to change this little credit text.
Thanks to the new divi version, you can easily change/edit divi footer credits from the theme customizer.
Just go to Appearance > Customize
From there go to Footer > Bottom bar
At the end of the section you can add your own custom text to replace the default Divi footer copyright info.
You can add some basic HTML over there as well.
Take a look at this video which shows you step by step how to change divi footer credits: