বাংলা টিউটোরিয়ালঃ https://obiplabon.im/173/wordpress-comment-form-customization/

wp-comment-form-customization-2.php

<?php
// Way Two
/**
 * Set comment textarea to the bottom of comment form
 * only works with WordPress version >= 4.4
 * @param array $fields Comment form inputs
 */
function op_change_comment_textarea_position( $fields ) {
	$comment = array('comment' => $fields['comment'] );
	unset( $fields['comment'] );
	return array_merge( $fields, $comment );
}
add_filter( 'comment_form_fields', 'op_change_comment_textarea_position' );

wp-comment-form-customization-1.php

<?php
// Way One
/**
 * Set comment textarea to the bottom of comment form
 * only works with WordPress version >= 4.4
 * @param array $fields Comment form inputs
 */
function op_change_comment_textarea_position( $fields ) {
	$comment = array( 'comment' => $fields['comment'] );
	return array_merge( array_diff_key( $fields, $comment), $comment );
}
add_filter( 'comment_form_fields', 'op_change_comment_textarea_position' );