I wish to update the mySql tables column of information type timestamp by hand through my PHP code . Can u please let me know how to achieve that.

Make use of this query:

update `table` set date_date=now();

Sample code could be:

$con = mysql_connect("localhost","peter","abc123");
if (!$con)
  die('Could not connect: ' . mysql_error());

mysql_select_db("my_db", $con);

mysql_query("update `table` set date_date=now()");