To continue running your ad, you will need to either edit the Page's country and/or age settings or edit the targeting of your ad.
You can edit your Page settings by visiting your Page Manager, selecting the related Page, and clicking on "Edit Page." Then click on "Settings" and you'll be able to change your Page's restrictions.
Alternatively, you can edit an ad by clicking "Edit Ad" below the ad preview in your account. This will take you to the ad creation page with the details from the ad already filled in, and give you the opportunity to make changes to your targeting. Your revised ad will be paused until it is reviewed by Facebook representatives.