How to get TYPO3 settings in the utility files?

You can add below line in the your controller.

$objectManager = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance('TYPO3\\CMS\\Extbase\\Object\\ObjectManager');    
$configurationManager = $objectManager->get('TYPO3\\CMS\\Extbase\\Configuration\\ConfigurationManager');
$setting = $configurationManager->getConfiguration(\TYPO3\CMS\Extbase\Configuration\ConfigurationManagerInterface::CONFIGURATION_TYPE_SETTINGS);   
$ts_config = $setting['plugin.']['tx_xxxx.']['settings.']['storagePid'];

I think it will helpful to you. You can also used this typo3 settings in the services files as well.

The above method works only in controller or services class try below it will work in any PHP files in Extension.

$objectManager = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance('TYPO3\\CMS\Extbase\\Object\\ObjectManager');
$configurationManager = $objectManager->get('TYPO3\\CMS\\Extbase\\Configuration\\ConfigurationManager');
$extbaseFrameworkConfiguration = $configurationManager->getConfiguration(\TYPO3\CMS\Extbase\Configuration\ConfigurationManagerInterface::CONFIGURATION_TYPE_FULL_TYPOSCRIPT);
$storagePid = $extbaseFrameworkConfiguration['plugin.']['tx_guesthouse_guesthouse.']['settings.']['storagePid'];