It’s possible to target anyone who's ever interacted with your brand’s events on Facebook.
To target these fans, make sure you have Page Advertiser or Page Admin access to the Facebook Page of the brand.
In the Audiences section of Facebook Ads Manager, create a custom audience made of fans who have interacted with the Facebook Events of the brand. You can do this by clicking on “Create Audience,” followed by “Engagement,” followed by “Event."
From there, select the page from which you’d like to pick events, in addition to the related events you'd like to target fans from:
Import that custom audience into the service by pressing “Add New,” “Facebook,” “Facebook Custom Audience,” followed by selecting the audience name in the “Template Options” section: