Place this file in your (Contao based) website's root folder and update your username in line 16. Then run it from the browser and log in to the backend using the password "random".

reset.php

<?php
 
define('BYPASS_TOKEN_CHECK', true);
require('system/initialize.php');
 
class Reset extends Frontend {
  public function __construct() {
    parent::__construct();
    $this->import('Database');
  }

  // 1. resets user's password to temporary to "random"
  // 2. forces to change on login
  // 3. if account was locked before, it's free now
  public function run() {
    $username = "YOUR_USERNAME"; // << set this to your username, obviously
    $newPassword = sha1("random"); // thanks @aschempp for this addition

    $this->Database->prepare("
        UPDATE tl_user
        SET password = ?
        , pwChange = 1
        , locked = 0
        WHERE username = ?
    ")->execute(
        $newPassword,
        $username
    );
  }
}
 
$reset = new Reset();
$reset->run();
echo "Go ahead and re-set a new password!";
?>