Issue [Solved] Missing comment form

The documentation is updated as well. 

@asti Hi Asti,

Thanks so much for your help.

I now managed to try Tip 2 but it still hasn't worked.

I am now on Fixing Tip 5 here: https://wpdiscuz.com/docs/wpdiscuz-7/getting-started/missing-comment-form/

From the screenshot, I don't understand how I get to that option on my Wordpress site. Please can you give more clarity / instruction how I find it.

Secondly, it says:

If there is no any settings to enable comments, you can use WordPress add_post_type_support() function. You can simply add the following to your active theme functions.php file:

function comment_support_for_my_custom_post_type() {
     add_post_type_support( 'my_post_type', 'comments' );
}
add_action( 'init', 'comment_support_for_my_custom_post_type' );

Where do I find the "fuctions.php" file? And where exactly do I add those code?

Thanks