Fix a URL/permalink/slug issue with PHP template

We have a custom PHP template in our WordPress theme, but the developer made it only work with a slug in front, but we cannot have it with a slug as this is a website that's been around for years and we cannot change the permalinks.

We need this error corrected as the previous developer refuses as they do not know how to remove the slug.

This is for someone who knows PHP. It should be super quick to remove the slug if you know what you're doing.

I can share the functions.php file so you can check beforehand what the issue is.