To schedule a job in a workflow to run every 30 days, follow these steps:

1. Go to the "Workflows" section in the sidebar.
2. Find the job you want to schedule in the "Name" column on the "Jobs" tab and click on it.
3. In the "Job details" panel, click on "Add trigger".
4. Select "Scheduled" as the trigger type.
5. Specify the period as "Monthly" and choose the starting time and time zone.
6. Click on "Save".

Example of a cron expression for running a job every 30 days:

0 0 1 */30 * ?

Please note that the cron expression may vary depending on your specific scheduling requirements and the platform you are using.