[HELP OJS 3] How to get custom block by name in coding?

I want to retrieve the content of custom block created by custom block manager plugin.
How to get the custom block by name in my theme code ?
Is there any code example on how to do it ?

already tested by using this code :
$metricsDao = DAORegistry::getDAO('MetricsDAO');

$listPlugin = $metricsDao->retrieve(
		"SELECT plugin_name, setting_name, setting_value FROM plugin_settings WHERE  (context_id='?') AND (setting_name='blockContent') ", (int) $currentJournalId

But I am not sure what DAORegistry::getDAO used for? since I would doing query on plugin table retrieve rather than Metric table

and as I retrieve the setting_value I got this value :

what is s:3 is about since as I explore the code number of s is always different on every block?