The 'Anti Ad Block Fallbacks' option is under the 'Monetizations' tab:
This is your All Fallbacks page where you can create geo-specific fallbacks for visitors that use Adblocking software. Start by clicking on the 'Add New' button.
The Add Fallbacks page sends visitors that use Adblocking to alternative (static) landing pages. Choose a Platform, Geos, Date Range and Static Landing Page URL. Don't forget to click on 'Add' on the bottom of the page!
After you click on 'Add' you're done! Good job!