Before you start
Ensure you have a segment from Alli Audiences activated to Facebook. You can find a tutorial on https://agencypmg.atlassian.net/wiki/pages/resumedraft.action?draftId=2072871135 at the link.
Navigate to a new ad set or edit an existing one in Facebook Ads Manager.
When selecting an audience to target for a new or existing ad set, look up your custom audience in the search bar.
Lookalike audiences created from a segment will also appear here. Please visit How-to Create a Lookalike Audience from an Activated Segment in Facebook for more on how to create one.
There are a number of steps for trafficking ads in Facebook not covered here, but now you know where to look to find your Alli Audience segment in the Facebook UI for targeting!