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.
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.