SELECT Id, Parent.RecordTypeId FROM FeedItem WHERE Type='EmailMessageEvent' AND Visibility!='AllUsers' AND Parent.Type = 'Case' AND Parent.RecordTypeId = '01258000000cZYOAA2'

global class EmailFeeditemBatch implements Database.Batchable<sObject>, Schedulable{

global Database.QueryLocator start(Database.BatchableContext BC){
    RecordType rt = [SELECT ID FROM RecordType WHERE DeveloperName = 'Support' AND SobjectType =  'Case' LIMIT 1]; //PUT THIS UP

    String  query = 'SELECT Id, Parent.RecordTypeId FROM FeedItem WHERE Type='EmailMessageEvent' AND Visibility!='AllUsers' AND Parent.Type = 'Case' AND Parent.RecordTypeId = ''+rt.Id+''';
    System.debug(query);
    return Database.getQueryLocator(query);
}


global void execute(Database.BatchableContext BC, List<FeedItem> scope){

    List <FeedItem> feedItemToUpdateList = new List<FeedItem>();
    for(FeedItem feedItem_i : scope){
            feedItem_i.Visibility = 'AllUsers';
            feedItemToUpdateList.add(feedItem_i);
    }
    if (feedItemToUpdateList.size()>0){
        update feedItemToUpdateList;
    }
}

global void finish(Database.BatchableContext BC){

}

global void execute(SchedulableContext sc) {

    database.executeBatch(new EmailFeeditemBatch(), 5);
}