I want to add some codes on my site, tell me is it safe?

Hello! Sir,

I want to add this code on “Theme editor” option but I didn’t find that option on “Appearance” section please tell me where is that option. And is that safe to add this code to my site? This is the code that disables the website URL option from the comment section.

// Disable Comments URL field
function jlwp_disable_comment_url($fields) {
unset($fields[‘url’]);
return $fields;
}
add_filter(‘comment_form_default_fields’,’jlwp_disable_comment_url’);

Thanks! Rohit S