When you have rented out your rentable, you have to mark your ad as rented out.
You do this by going to "Advertised rental properties" in the menu or by pressing the icon with two small houses on it. This is where you can get an overview of your ads and also change the status of your ad.
Click on the three dots on the line where the ad is now rented and needs to be updated (these are on the far right).
With the new status, the ad can no longer be seen by housing seekers on the portal, but the information is saved so that you can use it again if the need to rent out the home comes back later.