During the onboarding process, you will be required to select your primary Facebook Business Page as the page that will display all ads you purchase.
Please note: you must be an Admin of your Business Page in order for it to appear as an option. Your business page must also not be "owned" by any third party in order for it to appear.
To change your business page:
Click on Account tab in your Walled Garden Dashboard.
Select drop down menu of Business Pages
Select the Business Page you would like to use.
Another way to change your Business Page is during the ad creation step.
Click on the Business page icon above the ad editor.
Select desired business page.