Change Post Meta Order to Byline Then Date

Right now the post meta below my post titles on single post pages is "Date by Author."

I'd like it formatted at "by Author | Date"

I tried creating an element using the following and setting it to display after entry titles:

add_filter( 'generate_header_entry_meta_items', function() {
    return array(
        'author',
        'date',
       
    );
} );

I set it to execute PHP.

But this isn't working. It's just outputting the code itself.

The site's in maintenance mode during the changeover, but I'm linking a screenshot.

Any help is appreciated.

Thanks!