Update bulk post using wp_update_post().

bulk-post-update.php

<?php

$ids = array(18821,18811,18817,18805,18807,18777,18774,18775);

foreach ($ids as $key => $id) {
	$my_post = array(
		'ID'        => $id,
		'tax_input' => array( 
			'<taxonomy-name>' => array( `<tax-id1>`, `<tax-id2>`, `<tax-id-n` ),
		),
	);

	// Update the post into the database
	wp_update_post( $my_post );
}