date_date_set(object,year, month,day)

<?php
   //Creating a date
   date = new DateTime();
   //Setting the date
   date_date_set(date, 2019, 07, 17);   
   print("Date: ".date_format($date, "Y/m/d"));
?>

Date: 2019/07/17

<?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_date_set(date_time_Obj, 2015, 11, 25 );   
   print("Modified Date: ".date_format($date, "Y/m/d"));
?>

Original Date: 1989/09/25
Modified Date: 2015/11/25

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

Date: 2020/03/17

$dateSrc = '2005-04-19 12:50 GMT';
$dateTime = date_create( $dateSrc);;
# Now set a new date using date_date_set();
date_date_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->setDate( 1999, 10, 12);

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

New Formatted date is 2000-12-12T12:50:00Z
New Formatted date is 1999-10-12T12:50:00Z