It's not advisable to just change the dates of an old ad and re-publish it. By now it will be well down the list as many new ads have come after it. It's best to "create a new ad from an old ad". When you do the new ad will go to the top of the list and all sitters for your location will be notified. To create a new ad, when logged in on the Mindahome website and looking at your 'Dashboard' page, at the bottom you will see a "Create new listing" button. When you click it you will be given the option to create a new ad from the old one. When you choose that option all the text and images from the old ad will show in the new ad, you will just need to enter the new start and end dates.