Thank you for reaching out to the Community for assistance!
You can re-start callout with the Start Callout button on the job detail page if the status of the job has gone unfilled.
The Start Callout button displays if the job status is Stopped, Unfilled, or NSR (no substitute required) during a callout period. Selecting this button re-opens the job for the callout.
Please let us know in case of further queries.