$args = array(
'post_type' => 'namaste_course',
'post_status' => 'publish',
'posts_per_page' => -1,
);
$post_query = new WP_Query( $args );
if ($post_query->have_posts()) {
global $post;
$field_key = "field_59654068371a3";
$value = true;
while ($post_query->have_posts()) {
$post_query->the_post();
update_field( $field_key, $value, $post->ID );
}
wp_reset_postdata();
}