Follow the directions to sign up for a make up class. This will also allow you to enter in the class which you are missing, which helps us create spaces for other make ups! You don't need to have your log in information, just click on the "continue without an account" button, and follow the prompts.
If you would like a makeup in the next few days, just follow the prompts in the default "makeups by availability" tab. if you need one several weeks out, just change the date parameters, and then select the class that you want to show up for.