StitcherAds does not allow new adsets to be created and added to existing campaigns.
Some advertisers create new adsets in existing campaigns to facilitate reporting requirements. However, we recommend creating all new adsets in new campaigns and using the extensive reporting functions in StitcherAds to group campaigns for realtime reporting and analysis. This will allow you to easily compare the performance of all of your campaigns.
You can easily group campaigns with similar attributes together in a report which will provide you with a consolidated view.
Simply, navigate to Campaigns>Overview and then tick the box beside the campaign names you want to select. Next Click on the "Add to Report" button and either create a new report or add the campaigns to existing reports.