How can I edit comment notification email content?

You can apply a filter to comment_notification_text:

1525            /**
1526             * Filter the comment notification email text.
1527             *
1528             * @since 1.5.2
1529             *
1530             * @param string $notify_message The comment notification email text.
1531             * @param int    $comment_id     Comment ID.
1532             */
1533            $notify_message = apply_filters( 'comment_notification_text', $notify_message, $comment->comment_ID );

If you have extensive changes to make, since the function containing that hook is pluggable, you may find it easier to replace the entire function.