To add to cadfile's advise above, in the blank functions.php file you can enter the following at the top:
After that, you can copy and paste the original function twentytwelve_entry_meta code which starts with the line:
if ( ! function_exists( 'twentytwelve_entry_meta' ) ) :
All the way until (and including) the following lines:
After pasting the code, look for the section of the code that starts with the comments:
// Translators: 1 is category, 2 is tag, 3 is the date and 4 is the author's name.
and modify the text "This entry was posted in..." accordingly. After making the change, add the following closing PHP tag all the way at the bottom of the file:
and press Update File to save the child functions.php file. If you get a blank page, that means that you may have pasted something incorrectly; otherwise check a post on your site to see if the change took effect.
If you do get a blank page after the file update, you may need to go to your hosting control panel's file manager or a file transfer program to delete the child functions.php file from the child theme folder and start over, or if your hosting control panel has a code editor, you can simply edit the file by deleting what you pasted, and go back to the WordPress Dashboard theme editor and start over.