You can edit your job ad at any time. To edit your ad, go to your Dashboard and click on the Job Ad tab.
(The button of the Job Ad tab on mobile site)
You will be directed to the My ads page. Click on the 'edit job ad button' to make changes to your ad. If you want to hide/unhide your ad from the public list, simply click on the button next to 'Ad listed online' to change the display status.