(ISC)² does not offer Online exams. It was trialed earlier this year and due to cheating, it was decided that in-person would remain the only option.
You probably need to "reschedule" your exam, which according to the contact page is done by PearsonVue, not (ISC)². This needs to be done before the fact. Doing it after you have missed the appointment is a much harder problem to cheaply solve. There is a "rescheduling fee", which historically has been waived for things like government shutdowns and testing-center closures. Make sure you discuss this when rescheduling with PearsonVue.
Tagging "email@example.com" is not the same thing as emailing or calling them. The official ways of contacting them can be found under "exam administration" on their "Contact Us" web page (scroll to the bottom of this page). Please be aware that with the holidays approaching, it is likely that nobody will be in the office until after the New Year.