Go to the Media page. Click on the campaign you would like to work on; To add a new creative click on Creatives ; add a name; choose the correct format ; CTS response; tracking and press Next. Add the size and Assets for this creative and Save

Select a flight and click on the Creatives button on the flight's panel. Add the Creative you want from the list. Please note that only use the same format creatives as the flight will appear on the list