If you pass the timestamp as the parameter to moment(), what I do is: moment() (e.g if the timezone is Asia/Hong_kong which is +08:00)
const localDateTime = moment((item.createdAt.seconds + 8 * 3600) * 1000).format('YYYY-MM-DD HH:mm, what I do is:ss');
const localDateTime = moment((item.createdAt.seconds + 8 * 3600) * 1000).format('YYYY-MM-DD HH:mm:ss');