Login to Ad Manager. Scroll down to the bottom of the page and click on:

Click Zone Configuration on the next page:

Make sure you're in the right web property. If you're not, just click on the drop-down menu and select the property you wish to work on:

Once you have the right property selected, scroll down to the zone you wish to edit and click the pencil icon:

Edit as necessary the name or url and make sure the  status of the zone is set to active by clicking the check box next  to Is Active then click the Save button:

That's it.