date_isodate_set(object,year, week,day)

<?php
   //Creating a date
   date = new DateTime();
   //Setting the ISO date
   date_isodate_set(date, 2019, 03, 3);   
   print("Date: ".date_format($date, "Y/m/d"));
?>

Date: 2019/01/16

<?php
   //Date string
   date_string = "25-09-1989";
   //Creating a DateTime objectdate_time_Obj = date_create(date_string);
   print("Original Date: ".date_format(date_time_Obj, "Y/m/d"));
   print("\n");
   //Setting the date
   date = date_isodate_set(date_time_Obj, 2015, 4, 3 );   
   print("Modified Date: ".date_format($date, "Y/m/d"));
?>

Original Date: 1989/09/25
Modified Date: 2015/01/21

<?php
   //Creating a date
   date = new DateTime();
   //Setting the date
   date_isodate_set(date, 2019, 15, 17);   
   print("Date: ".date_format($date, "Y/m/d"));
?>

Date: 2019/04/24

<?php
   dateSrc = '2005-04-19 12:50 GMT';dateTime = date_create( dateSrc);;

   # Now set a new date using date_isodate_set();
   date_isodate_set(dateTime, 2000, 12, 12);

   echo "New Formatted date is ". dateTime->format("Y-m-d\TH:i:s\Z");
   echo "  
";

   # Using second function.dateTime = new DateTime(dateSrc);dateTime->setISODate( 1999, 10, 12);

   echo "New Formatted date is ". $dateTime->format("Y-m-d\TH:i:s\Z");
?>

New Formatted date is 2000-03-31T12:50:00Z
New Formatted date is 1999-03-19T12:50:00Z