set_tterm_from_custom_fields.php

<?php
	$args = array(
		'post_type'      => 'works',
		'posts_per_page' => -1,
	);
	$set_tax_posts = get_posts( $args );
	foreach( $set_tax_posts as $post ) {
		setup_postdata( $post );
		$post_id = $post->ID;
		// ここにメディアカスタムタクソノミーを
		$tax_array = array();
		$textfield_common2 = get_post_meta( $post_id, 'textfield_common2', true );
		$tax_array = explode( ',', $textfield_common2 );
		var_dump( $tax_array );
		wp_set_object_terms( $post_id, $tax_array, 'media', false );
	}
?>