Use this to update your copyright for the Sydney Theme after you’ve followed the original tutorial. Download the child theme at NYC TECH CLUB (link below)
Text link: http://www.nyctechclub.com/using-a-child-theme-for-sydney-theme-footer-modification/
There are a few steps involved to get your site to look exactly like it does before uploading the child theme. Make sure you watch! The only thing you need to do is change your settings in the customize tab to however you set them before.
None of your parent customizations changed, so you can always go back and references those by activating the parent sydney theme and clicking on customize to take a look.