if($_SESSION['email'] == 'admin17598@outlook.com'){
  echo 'a link to a file that i will use to insert and update my tables'
}

<?php
require_once '../../db.php';
session_start();

if( $_SESSION['logged_in'] != 1 || $_SESSION['email'] != 'admin17598@outlook.com'){

$_SESSION['message'] = "Algo deu errado :/";
header("location: ../error.php");
exit;

}else {
 $username = $_SESSION['username'];
}
?>

<?php

if($_SERVER['REQUEST_METHOD'] == 'POST'){

$email = trim($_POST['email']);

try{
  $ckeckEmail = $conn->prepare("SELECT `email` FROM users WHERE `email` = :email");
  $ckeckEmail->bindValue(':email', $email);
  $ckeckEmail->execute();
  $user = $ckeckEmail->fetch(PDO::FETCH_ASSOC);
  $RowCount = $ckeckEmail->rowCount();
} catch (PDOerrorInfo $e){}

  if( $RowCount == 0 ){
   // User doesn't exist
    $_SESSION['message'] = "Não existe um usuário com este e-mail.";
    header("location: error.php");
     exit;

  } else{ // User exists

      if( password_verify($_POST['password'], $user['password'])){
        $_SESSION['email']  = $user['email'];
        $_SESSION['user_id'] = $user['user_id'];
        $_SESSION['first_name'] = $user['first_name'];
        $_SESSION['last_name'] = $user['last_name'];
        $_SESSION['username'] = $user['username'];
        $_SESSION['img'] = $user['img'];
        $_SESSION['capa'] = $user['capa'];
        $_SESSION['logged_in'] = true;
        header("location: ../?p=profile");
        exit;
      } else {
          $_SESSION['message'] = "Password is incorrect";
          header("location: error.php");
           exit;
        }
    }
}

$conn = NULL;

<?php

$img = rand(1,44);
$capa = rand(1,36);
$first_name = trim($_POST['first_name']);
$last_name = trim($_POST['last_name']);
$username = trim($_POST['username']);
$email = trim($_POST['email']);
$password = password_hash($_POST['password'], PASSWORD_BCRYPT);
$hash = md5( rand(0,1000) );

// Check if user with that email already exists
$result = $conn->prepare("SELECT `email` FROM users WHERE `email` = :email");
$result->bindParam(':email', $email);
$result->execute();
$RowCount = $result->rowCount();

if ( $RowCount > 0 ) {
    $_SESSION['message'] = 'Já existe um usuário com este e-mail!';
    header("location: error.php");
     exit;
}
else {
    $sql = "INSERT INTO users (dataR, ultima_atividade, first_name, last_name, username, img, capa, email, password, hash) VALUES (NOW(), NOW(), :first_name, :last_name, :username, :img, :capa, :email, :password, :hash)";
    $sql = $conn->prepare($sql);
    $sql->bindParam(':first_name', $first_name);
    $sql->bindParam(':last_name', $last_name);
    $sql->bindParam(':username', $username);
    $sql->bindParam(':img', $img);
    $sql->bindParam(':capa', $capa);
    $sql->bindParam(':email', $email);
    $sql->bindParam(':password', $password);
    $sql->bindParam(':hash', $hash);
    $sql->execute();
    $_SESSION['message'] = 'You account was created!';
    header("location: success.php");
}
$conn = NULL;

<li class="pt-1 pb-2 liInfUs">
  <h6>Nome: <?php echo htmlentities($first_name, ENT_QUOTES, 'UTF-8', false).' '.htmlentities($last_name, ENT_QUOTES, 'UTF-8', false); ?></h6>
  <h6 class="quicksand300">Email: <?php echo htmlentities($email, ENT_QUOTES, 'UTF-8', false); ?></h6>
</li>
<?php if($_SESSION['email'] == 'admin17598@outlook.com'){
  $countUserOLN = $conn->query("SELECT * FROM users WHERE ultima_atividade >= NOW()-600");
  $rstq = $countUserOLN->rowCount();
  $countUserAll = $conn->query("SELECT * FROM users");
  $rstAll = $countUserAll->rowCount();
?>
  <li class="d-flex">
    <h6 class="mr-3"><a href="verify/criar/painel.php" style="color: #21D3FF">Painel</a></h6>
    <h6 class="quicksand300 mr-3">Users: <?php echo $rstAll ?></h6>
    <h6 class="quicksand300">Online: <?php echo $rstq ?></h6>
  </li>
<?php } ?>