common\models\User::removePasswordResetToken PHP Method

    public function removePasswordResetToken()
    {
        $this->password_reset_token = null;
    }

 /**
  * Resets password.
  *
  * @return boolean if password was reset.
  */
 public function resetPassword()
 {
     $this->_user->setPassword($this->password);
     $this->_user->removePasswordResetToken();
     if ($this->_user->save()) {
         $this->_user->sendPasswordChangedEmail();
         return true;
     }
     return false;
 }