Hi Tom,
Thanks for reaching out! I will try to help with your question.
There is a filter on the output of that function. You can replace what this returns from your functions.php file.
In this example, I have copied the original function’s logic into our custom filter callback. You would just need to replace ‘path/to/your-custom.gif’ with the full path to the image you want to use instead.
https://gist.github.com/skyshab/484c3c6bfeac4065ca7273737567284d
So just add this to your child theme’s functions.php, and modify it to use the image you want.
Hope that helps! Please let me know if you have additional questions about this.
Thanks,
Sky