It may take a while to schedule a tax appointment due to limited space.
Here is the link to the online scheduling system: https://booknow.appointment-plus.com/43rspqeq/
On the system, you can select the campus you are on and your employment type. From there, you can find openings to schedule an appointment.
If you are still having difficulties, you can email IntlTax@cu.edu to speak with an international tax professional.