<?php

$myArray = [
        "fname" => "Sudhir",
        "lname" => "Gour",
        "age" => 27,
        "city" => "Jaipur",
        "state" => "Jaipur",
        "country" => "India"
    ];
    
$arrayNewKeys = [
    "first_name" => "Sudhir",
    "last_lname" => "Gour",
    "new_age" => 27,
    "city" => "Jaipur",
    "state" => "Jaipur",
    "country" => "India"
];

print_r(array_diff_key($myArray , $arrayNewKeys));