If an Organisation has updated a position e.g. change some text in the job advert, or a job category etc they sometimes need to unpost the position and repost it again for the details to pull through. Or alternatively they could have withdrawn it totally for various reasons (you can contact the recruiting Organisation for specific information).

If the position is still being advertised all you need to do is search and find the job advert and reapply for the job.

The same details will pull through and you can continue from there.