If you have missed a CBTF Online exam for any reason, or if your exam could not be completed, then:
Contact your professor immediately. You should include your NetID, a precise description of which exam you missed (e.g., "Exam 2 for ENG 100") and a clear explanation of what happened.
Do not contact the CBTF directly. Your professor will need to make the decision about how to proceed. You will not be able to take the exam with the CBTF for at least two business days. There is no way to be rescheduled to take the exam with the CBTF later the same day or the next day, but you should contact your professor as soon as you are aware of the situation.