Add this code to the child theme functions.php:

add_filter( 'register_post_type_args', 'scent_register_post_type_args', 10, 2 );
function scent_register_post_type_args( $args, $post_type ) {

    if ( 'model' === $post_type ) {
        $args['rewrite']['slug'] = 'NEW_SLUG';

    return $args;

Replace the NEW_SLUG with your own.

Note, that the code must be wrapped in the opening <?php and closing ?> along with the other PHP code in the file.

Important! After you add the code and see that it is applied (slug changed), there is still one thing to do. Go to Settings > Permalinks, and without doing anything, just click "Save Changes" button on that page.