Divi > Theme Customizer > Footer > Bottom Bar
Unfortunately, there is no option to center the footer credits. But with this CSS snippet, you can center these credits.
Place this snippet in Divi > Theme Options > CSS or in your Divi child theme. The first part of the snippet centers on the footer credits and the second part of the snippet is for the social media icons in case you are using those.
In case you want to create an entire custom Divi footer you can follow this tutorial how to create a custom Divi footer.
You can also use one of the Divi footer layout packs available on the marketplace.