how to add input in form 'Y-m-d H:s:i' html code example

Example 1: php get current date and time

$today = date("F j, Y, g:i a");   // October 30, 2019, 10:42 pm
$today = date("D M j G:i:s T Y"); // Wed Oct 30 22:42:18 UTC 2019
$today = date("Y-m-d H:i:s");     // 2019-10-30 22:42:18(MySQL DATETIME format)

Example 2: php timestamp to date

<?php 
echo date('m/d/Y H:i:s', 1541843467); 
?>