Unable to store Trigger with name: 'trigger1' and group: 'group1', because one already exists with this identification

boolean flag = scheduler.checkExists(trigger.getKey());
if (!flag)
{
    scheduler.start();
    scheduler.scheduleJob(job, trigger);
}
else
{
    Trigger trigger1 =TriggerBuilder.newTrigger().withIdentity("schedulerJobTrigger1", "group1").withSchedule(schedBuilder).build();;
    scheduler.start();
    scheduler.scheduleJob(job, trigger1);
}