How do I implement onclick forgotten password function properly?

<pre><div class="container">
  <div class="login">
  
    
  	<h1 class="login-heading">Please login.</h1>



      <form method="post" action="login.php">
        
        <input id='email1' type="email" name="email" placeholder="Email Adress" required="required" class="input-txt" onchange="checkuser();"  />  
        <input id='pass1' type="password" name="password" placeholder="Password" required="required" class="input-txt" />
		
        <input type"button" name="forgot" class="btn" data-target="#pwdModal" data-toggle="modal" value="Forgot password?">
<div id="pwdModal" class="modal fade" tabindex="-1" role="dialog" aria-hidden="true">
  <div class="modal-dialog">
  <div class="modal-content">
      <div class="modal-header">
          <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
          <h1 >Forgot My Password?</h1>
      </div>
      <div class="modal-body">
          <div class="col-md-12">
                <div class="panel panel-default">
                    <div class="panel-body">
                        <div class="text-center">
                          
                          <p>If you have forgotten your password, simply click on the button below to fetch your password from the server!</p>
                            <div class="panel-body">
                                <fieldset>
                                    
                                    <div id="forgot">
			 <input type="button" class="btn" value="Get my password" tabindex="2" onclick="forgotten();"><br> <br>
                         <p id="pass" style="border-style:dotted;border-color:coral; border-radius:5px;"></p>
             <script>
			 var forgot_email = document.getElementById("email1");
             

             var request1 = new XMLHttpRequest();

             //fetching the password based on the email address
             request1.open("GET", "storedata.xml", false);
             request1.send();

             var xml1 = request1.responseXML;
             var users1 = xml1.getElementsByTagName("data");
			 
			 function forgotten {
             for(var i = 0; i < users1.length; i++) {
             if (forgot_email == users1[i].getElementsByTagName("email2").value {
             var forgotten_pass= users1[i].getElementsByTagName("pass2").value;
			 break;
             }
    
             } 
			 document.getElementById("pass").innerHTML=forgotten_pass;
             }
			 </script>
			 
	
                
			 </div>   
                                </fieldset>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
      </div>
      <div class="modal-footer">
          <div class="col-md-12">
          <button class="btn" data-dismiss="modal" aria-hidden="true">Cancel</button>
		  </div>	
      </div>
  </div>
  </div>
</div>
			
             <button type="submit" class="btn" name="ok" id="b1" >Sign in </button> <br> <br>
	
      </form>
	  
	  <script>
             
//checking if the email exists in the server xml or not
var first_email = document.getElementById("email1");

var request = new XMLHttpRequest();

//creating an array of the existing emails
request.open("GET", "storedata.xml", false);
request.send();

var xml = request.responseXML;
var users = xml.getElementsByTagName("data");
const existingEmails = [];

for(var i = 0; i < users.length; i++) {
    const emailTag = users[i].getElementsByTagName("email2");
    const email = emailTag[0].childNodes[0].nodeValue;

    existingEmails.push(email);
}

function checkuser() {
 if(existingEmails.includes(first_email.value)) {
      email1.setCustomValidity('');
 }
 else {
 email1.setCustomValidity('Sorry but this email address doesnt exist in the server.');
 }
}


</script>        
	  	 
 
  </div>
</div>

<pre><?xml version="1.0" encoding="utf-8"?>
<document>
<data><fname>Group</fname><lname>Project</lname><email2>webuy55@gmail.com</email2><pass2>teamproject55</pass2></data>
<data><fname>Sam</fname><lname>Kim</lname><email2>samkim@gmail.com</email2><pass2>abcd1234</pass2></data>
<data><fname>Harold</fname><lname>Pain</lname><email2>hpain@gmail.com</email2><pass2>abcd</pass2></data>
<data><fname>Ryan</fname><lname>Reynold</lname><email2>ryan@gmail.com</email2><pass2>123456</pass2></data>
<data><fname>Reece</fname><lname>Simpson</lname><email2>reece@gmail.com</email2><pass2>onlinestore</pass2></data>
<data><fname>Stefani</fname><lname>Germanotta</lname><email2>stef@gmail.com</email2><pass2>bbbcccddd</pass2></data>
</document>