How do I request an absence at Abercrombie Kids?

So I am a new employee, I have worked two shifts as a model (one of which was 2 hours over time) and I just received my schedule for this week. It consists of all call-ins. I have homecoming on the 20th and I can't figure out how to request an absence online. Should I call and ask my manager? I am afraid they will be mad and fire me or something. (note this is my first job)

You worked 2 ENTIRE SHIFTS and now need a day off?!?
Yeah, I think you are about to lose your job.