Once the Multi-Treatment Output is published, connect the feed link to your catalog in Commerce Manager.
Once connected, you can begin assigning specific treatments to appear within selected ads. Click on Assign Ads to open up a list of campaigns within your Ads Manager.
Select the campaign in the window that appears to view the ads and ad sets. Click on the catalog ad you'd like to apply a treatment to. Then select the treatment you'd like to use. Once the treatments are assigned and ready to go, Click Publish Assignments to push the treatments to Ads Manager.
You'll only need to assign a treatment once. Any updates made to the designs within the treatments can be pushed to Ads Manager by clicking Publish Updates in the main Output Feed options.