To quickly repost a job that has ended, simply go to the Jobs page located in the side navigation and click on "Repost a Job" in the top right hand corner - this will change the filter to Closed Jobs.
From here, choose the job you wish to repost. Next, you'll be taken to the Post a Job form to make any edits/updates you need to this specific post.
Click Review Your Job and if all looks good, click Checkout or you can select Make Changes to go back and edit your posting further.