Convert code to Virtuemart cron job

We have a small cron job running in Joomla 2.5 and Virtuemart 2. It works perfect, but not in my testing environment where I upgrade the site to Joomla 3.6 and Virtuemart 3. This job is to create an installable virtuemart plugin (or module) to run the cron job in Virtuemart 3. I added the current code (one php file) to this job. Cron job function: The cron job search for orders which not have status 'shipped' and occur in a custom table. Then it updates the orderstatus from to 'shipped' and add the tracking number from the custom table to the order comment field. When updating order status the customer is automatic receiving an email with tracking number.