If a unit has rented or sold, you can take it off the market by editing the status of the listing. Check out this article for more details: Managing the Availability Status of Your Listings
If however, your listing has not rented or sold and you would like to take it off the market, you can do so by clicking the Remove Unit button at the bottom of the listing:
Note: This will remove your listing from third party sites, but each site has their own methods of determining the status of a listing. If you would like your listing to reflect a particular off-market status, please reach out to each site directly.