The default Footer Credits can be changes in 2 ways.
Easy way using the Theme Customizer
Go to Divi > Theme Customizer > Footer > Bottom Bar > Edit Footer Credits and start typing your own credits. This will replace the default Divi Footer Credits.
Another way using Theme Builder
In the Divi > Theme Builder, we can create a footer template and add any modules to it. The footer template will replace the default footer. It can be used on all pages or on particular pages
More details about the Theme Builder can be found here.
Advanced way using a child theme
First you will need to have a working Child Theme.
Once the Child Theme is active the next step will be to install a 3rd party plugin which will allow you to create, delete, rename new PHP files.
Download and install the WPIDE plugin. Although the new WordPress File Editor is great is missing a few basic functionalities like:
the ability to create new files
rename a file
move files
The WPIDE plugin allows you to do that while having all the features that the WordPress File editor has.
Once the plugin is installed navigate to wp-content folder > divi folder and open the footer.php file and copy all of its PHP code.
Navigate to your Child Theme folder and create a new file:
Name the new PHP file footer.php and paste inside the code copied from footer.php of the parent theme.
In the code you have just pasted find this line of code:
echo et_get_footer_credits();
And replace that with:
<p id="footer-info">Your own copy right</p>
Save the file and you are done.