BBpress forum role change in bulk

bbpress_forum_role.php

<?php
add_action( 'wp', array($this, 'change_existing_user_forum_role') );

function change_existing_user_forum_role(){
    $args = array (
        'role'           => 'bbp_spectator',
    );

    $user_query = new WP_User_Query( $args );
    if ( ! empty( $user_query->results ) ) {
        foreach ( $user_query->results as $user ) {
            bbp_set_user_role($user->ID, 'bbp_participant');
            $user = new WP_User($user->ID);
            $user->remove_role('bbp_spectator');
            $user->add_role('bbp_participant');
        }
    }
}
?>