Custom post type and page with the same name

I had a problem related to my custom post type and my page, since they shared the same name and when I created page-<slug_name>.php WordPress got confused.

However, I found a solution here (19th post) : I found this : https://wordpress.org/support/topic/pages-and-custom-types-cannot-have-the-same-name-so-how-to-structure-permalinks?replies=20

However, I don’t understand where to add that code in my functions.php if I used CPT UI plugin to create my custom post types… So, I didn’t create the custom post type in my functions.php, but I made it over the CPT UI plugin in the admin panel.

How and where do I add that code then?

Thanks in advance!