If you previously closed or archived a job, you can re-open. Note however that you can't re-open a job you deleted.
First, browse to the navigation on the left hand side of your screen and select 'Manage Jobs' under the 'Jobs' section:
Locate the job you wish to re-open and click the three dots to the right of it. Then, click 'Open':
Your job is now live and will appear on your public facing jobs portal.