There are two options to run the bounce cron
1- You can run it instantly on the next cron execution by navigating to Settings -> Cron Settings and click on "Run" button.
2- Setup an additional cron in your server for the bounce processing individually on any frequency. E.g. look at the example below that process bounces after every 5 minutes.
*/5 * * * * php /path_to_mumara/cronjob/cron_bounce_processing.php