You receive your initial credentials via email at some point between after you take the exam and when your exam results are ready. You may receive your credentials at the same time as your exam results, or you may receive the credentials at some point before the exam results, depending on how your exam set is processed internally. So, make sure you have provided a real email address when you take the exam.
Be sure to update your address when you move, change email providers, or otherwise change your contact information. If you know other people who took the exam with you have received their credentials or exam scores but you haven’t, contact the exam staff and let them know where and when you took the exam. There may have been an error in your data that was submitted by the exam administrator.