Admin users can track attendance either of the Activities described below on several pages in the Admin Portal:
Ratios Page - Click on the Enrollee name to open up the timeline window where you can post an Activity.
Classes Page - Click on the timeline icon beside an Enrollee under a Class. This opens up the timeline window where you can post an Activity.
Activity Page - Click on an Enrollee on the left to open up their timeline.
Instructor Portal - As an admin, you can create an instructor profile for yourself via the Instructor page. Within the instructor settings, select "Can access all classes". See this support article for how to set up an Instructor profile.
For more details on how to manage attendance in the Instructor Portal, see this support article.