how to reschedule quartz job dynamically

Question

I am trying to update the quartz job scheduling dynamically:

Initially it is after every 3 minute, but dynamically i want to make it 1 min.

here's my quartz.xml and java file

quartz.xml

    <schedule>
        <job>
            <name>JOBNAME</name>
            <group>GroupDummy</group>
            <description>This is Job B</description>
            <job-class>in.xyz.MyClass.java</job-class>
        </job>

        <trigger>
            <cron>           
                <name>dummyTriggerNameB</name>
                <group>MYTRIGGER_GROUP</group>
                <job-name>JOBNAME</job-name>
                <job-group>GroupDummy</job-group>
                <cron-expression>0 0/3 * * * ?</cron-expression>
            </cron>
        </trigger>
    </schedule>

MyClass.java

    public void execute(JobExecutionContext arg0) throws JobExecutionException {
        Scheduler scheduler = new StdSchedulerFactory().getScheduler();
        CronTrigger cronTrigger = (CronTrigger) scheduler.getTrigger("dummyTriggerNameB", "MYTRIGGER_GROUP");
        CronExpression cronExpression = new CronExpression("0 0/1 * * * ?");
        cronTrigger.setCronExpression(cronExpression);
        scheduler.rescheduleJob("dummyTriggerNameB", "MYTRIGGER_GROUP", cronTrigger);
    }

I am trying the above java code to change the time from 3 minute to 1 minute dynamically but it is not happening "cronTrigger" is returning null.

Help to solve this problem so that i can reschedule dynamically.