Are you currently a student of the University of Antwerp?
Then you use the request "Re-enrolment" in your SisA self service to re-enrol after 15 July 2023 for the academic year 2023-2024. The instructions can be found in the helpdesk.
(Future) PhD students can still use the re-enrolment request in SisA for academic year 2022-2023 after obtaining a permission from the faculty.