Yes, you have to copy the whole footer.php file to your child theme's folder, and there, don't replace all the code, just that couple of lines that you have pasted in, in the rows about 19-24 (although your file can be a little bit different, regarding the row numbers).
Remember to activate the child theme so WordPress uses that, and not the original theme.
Let me know if you were able to make it work.
Cheers,
Toth Balint BT