How to apply "Pretty Permalinks" to standalone page?

I have turned on “Pretty Permalinks” and it works great. However, I created a standalone php page, e.g. cars.php and right now it shows up as:

https://www.example.com/cars.php

How can I make it show up like the URLs for the pages in WordPress like this:

https://www.example.com/cars/

Is this something that needs to be done .htaccess or do I need to write something into a WordPress PHP file?

Thanks!