How to modify WCMP Rest API response?

Finally I had solved it!

In the source code of the plugin “dc-woocommerce-multi-vendor”, I had viewed the class “class-wcmp-rest-vendors-controller.php” and figured out that they are using this filter in order to gather up the fields of the response:
apply_filters("wcmp_rest_prepare_vendor_object_args", array(...));

In the functions.php of the child theme I had written this code to edit the filter:

function modify_rest_api_vendor_response( $arg ) {
    $arg["shop"]["image"]=wp_get_attachment_url($arg["shop"]["image"]);
    return $arg;
}
add_filter( 'wcmp_rest_prepare_vendor_object_args', 'modify_rest_api_vendor_response', 10, 3 );

And now I can get the image URL

Hope that it could help somone…