autopopulate field

In reference to this topic,
https://www.ads-software.com/support/topic/populate-field-values?replies=7

and to this exemple on Caldera’s site
https://calderawp.com/doc/customizing-auto-populated-field-options-in-caldera-forms/

I still miss the point to where to put the filter in the code, in wich element ? In functions.php or in the plugin itself ? Or elsewhere

My code will be :

add_filter( 'caldera_forms_autopopulate_options_post_value_field', function( $value_field, $field ) {
    if( 'atelier' == $field[ 'slug' ] ) {
        $value_field = 'cout';
    }

    return $value_field;
}, 24, 2 );

Where atelier is the custom post type and cout the custom field. I can’t have COUT to be display in the autopopulate value option.

Thank you again for your time!

https://www.ads-software.com/plugins/caldera-forms/