public class LeadsCLASS{

    public static void OwnerUpdate(Lead[] ts){
        List<Event> aplist = new List<Event>();

        for(Lead t : ts){
            IF(
                (t.LeadSource == 'Telemarketing'&& t.OwnerId != '00G30000001iNeK' &&
                 t.OwnerId != '00G30000001iNtxEAE' && t.OwnerId != '00G30000001uiO5' &&
                 t.OwnerId != '00G30000001iCwM' && t.OwnerId != '00G30000001uh70' &&
                 t.OwnerId != '00G30000001iNt5EAE' && t.OwnerId != '00G30000001ui8wEAA' &&
                 t.OwnerId != '00G30000001iNuC' && t.OwnerId != '00G30000001iNsL' &&
                 t.OwnerId != '00G30000001iNvZ' && t.OwnerId != '00G30000001jtEi' &&
                 t.OwnerId != '00G30000001tiXR' && t.OwnerId != '00G30000001ui8w' &&
                 t.OwnerId != '00G30000001iNt5')
              )

            {List<Event> aps = [Select WhoId, Whatid, OwnerId from Event where WhoId = :t.Id];
               for (Event ap : aps){       
                      ap.OwnerId = t.OwnerId;
                      aplist.add( ap );
               }
            }
        }
        update aplist;

    }

//Test Method

    static testMethod void T1() {
        Id lId;
        Id eId;
        
         //CREATE 1 LEAD
     
        Lead l = new Lead();
        l.LeadSource = 'Telemarketing';
        l.lastname = 'Doe';
        l.company = 'Test Company';
        l.ownerId = '00530000003IFwV';
        l.status = 'Open';
        l.market__c = 'Atlanta';
        Database.insert(l);
        lId = l.Id;
    
          
        //CREATE 2 Event
    
          Event e = New Event ();
          e.DurationInMinutes     = 60;
          e.ActivityDateTime      = date.today();
          e.ownerId               = l.ownerId;
          e.WhoId                 = l.Id;
    
         Database.SaveResult result = Database.insert(e);
            eId = e.Id;
        
              update e;
          
         {List<Lead> aps = [Select Leadsource, owner_convert_queue__c, id, OwnerId from Lead
          where id = :e.whoId];
             system.debug('@@@apo=' + aps);
         }
    }

}

 Use that for the class and make sure the file name you give it is something that will be unique, for example LeadsCLASS.

trigger OwnerUpdate on Lead (after Update) {

Lead[] t = Trigger.new;
LeadsCLASS.OwnerUpdate(t);

}

Use that for the trigger and make sure the file name you give it is something that will be unique, go with LeadsUpdateTRIGGER.

It's good practice to suffix your triggers because if you write any visualforce pages, you'll also have controllers and you'll want to easily distinguish them. I'm thinking the name you chose for your trigger or class is already taken.