FB PHP SDK change unread message status to read and counting Unread Messages

I need some help after I could not able to find the solution for this. There is similar question here but no accepted answer. I am using FB PHP SDK v4.4.0 and now I am able to pull out all the conversations between other users and my page. However, I am wondering on how do I change the status of "unread" to "read". I want to pull the conversations and store them in MySQL. However, for performance-wise, I like to pull only the "unread" message instead of pulling everything. This makes the process slower due to the increasing number of conversations in the future.

Here is the part of my current code that I have that will list out all of the conversations in very sophisticated array:

FacebookSession::setDefaultApplication( $api_key, $api_secret );
$session = new FacebookSession($accessPageToken);
$request = new FacebookRequest($session, 'GET', '/me/conversations'); 
$Convs = $request->execute()->getGraphObject()->asArray();