How to display results of code before the_content in wordpress?

I have code which tests to see if we are on a page with the category term of case-studies and then displays a jQuery slider using the ACF gallery field. This technically works fine as you can see here:

https://www.immersivereality.co.uk/test-case-study/

But its appearing at the top and no matter where I add it in the single.php file its either right at the top or the bottom. I want to add add it in at the start of the content so it appears underneath the Title and meta data.

I have seen this code:

function prefix_add_content ($content){

$before = "This comes before the content.";
$after = "This comes after the content (like my Podcast badge).";
$content = $before . $content . $after;

return $content;
}
add_filter ('the_content', 'prefix_add_content');


which looks good but how do I inject the reults of the ACF code into the $before variable?

Regards,

David