welcome back to shortlearner.com, in this post we will see how to send forgot password on mail with the help of PHP.
So in the very step we establish our database connection in connection.php file than we include it in our send.php file.
connection.php

<?php
$server_name='localhost';
$user_name='root';
$password='root';
$db_name = "crud";
$con= mysqli_connect($server_name,$user_name,$password,"$db_name");
if(!$con){
 die('Could not Connect My Sql:' .mysql_error());
}
?>

index.php
Also Read :
PHP Login Script With Remember me.
Change password using javascript, php and mysqli.
Password and Confirm Password Validation Using JavaScript
Check Email is Already Registered in Database using Ajax and JavaScript.
How to hide extension of html and php file.?

<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<link rel="stylesheet" href="style.css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<!------ Include the above in your HEAD tag ---------->

<div class="container forget-password">
            <div class="row">
                <div class="col-md-12 col-md-offset-4">
                    <div class="panel panel-default">
                        <div class="panel-body">
                            <div class="text-center">
                                <img src="https://i.ibb.co/rshckyB/car-key.png" alt="car-key" border="0">
                                <h2 class="text-center">Forgot Password?</h2>
                                <p>You can reset your password here.</p>
                                <form id="register-form" role="form" autocomplete="off" class="form" method="post" action="send.php">
                                    
                                    <div class="form-group">
                                        <div class="input-group">
                                            <span class="input-group-addon"><i class="glyphicon glyphicon-envelope color-blue"></i></span>
                                            <input id="forgetAnswer" name="user_id" placeholder="Username" class="form-control"  type="text">
                                        </div>
                                    </div>
                                    <div class="form-group">
                                        <input name="btnForget" class="btn btn-lg btn-primary btn-block btnForget" value="Reset Password" type="submit" name="submit">
                                    </div>

                                </form>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>

style.css

body{
    background:#f3c538;
}
.forget-pwd > a{
    color: #dc3545;
    font-weight: 500;
}
.forget-password .panel-default{
    padding: 31%;
    margin-top: -27%;
}
.forget-password .panel-body{
    padding: 15%;
    margin-bottom: -50%;
    background: #fff;
    border-radius: 5px;
    -webkit-box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
}
img{
    width:40%;
    margin-bottom:10%;
}
.btnForget{
    background: #c0392b;
    border:none;
}
.forget-password .dropdown{
    width: 100%;
    border: 1px solid #ced4da;
    border-radius: .25rem;
}
.forget-password .dropdown button{
    width: 100%;
}
.forget-password .dropdown ul{
    width: 100%;
}

send.php

<?php
session_start();
include_once 'connection.php';
if(isset($_POST['submit']))
{
    $user_id = $_POST['user_id'];
    $result = mysqli_query($con,"SELECT * FROM user_details where user_id='" . $_POST['user_id'] . "'");
    $row = mysqli_fetch_assoc($result);
	$fetch_user_id=$row['user_id'];
	$email_id=$row['email_id'];
	$password=$row['password'];
	if($user_id==$fetch_user_id) {
				$to = $email_id;
                $subject = "Password";
                $txt = "Your password is : $password.";
                $headers = "From: password@studentstutorial.com" . "\r\n" .
                "CC: somebodyelse@example.com";
                mail($to,$subject,$txt,$headers);
			}
				else{
					echo 'invalid userid';
				}
}
?>