How can i delete all expired jobs?

You can set the “Delete Expired Jobs” filter to true by adding something like this to your theme’s functions.php or a core functionality plugin:

add_filter( 'job_manager_delete_expired_jobs', '__return_true' ); (notice return_false is preceded by two underscores.

There is a built-in 30-day delay, so only expired jobs that are older than 30 days expired will be deleted. That can be modified via the job_manager_delete_expired_jobs_days filter.

https://github.com/Automattic/WP-Job-Manager/blob/edf3cdceeabcad1e84b80d7827445fb8272081de/includes/class-wp-job-manager-post-types.php#L423