Thanks for your question about updating your copyright message in your blog. By default, if you have a licensed copy of BoldGrid, then the Footer option in the Customizer will allow you to remove the copyright information. If you are modifying the footer, then you need to find the footer code where you changed it and then update it as you need. The location you have indicated in your question is not the correct place to make the update. For CSS changes, you can use the Chrome browser to find the location of your footer code. Click on the link to learn how to use the Inspect option for that purpose. You may also need to look at the theme that you are using and then find the footer code there. You can use the WordPress editor (BoldGrid removes the default link, but you can still access it here (be sure to use your domain name in the URL): http://your-domain-name/wp-admin/theme-editor.php in the WordPress dashboard. Keep in mind that any code changes you make directly to the theme will be removed by a theme update. You can only avoid this using child theme or by using the BoldGrid Customizer’s CSS/HTML Editor to add code.
I hope that helps to answer your question! If you require further assistance please let us know!