If you miss an exam due to sickness or injury, then you should obtain medical evidence and apply for exceptional circumstances.
If you miss an exam due to a bereavement or another personal issue, then you should obtain suitable evidence and apply for exceptional circumstances.
If you miss an exam without a good reason, then you will get a zero mark for the examination. Please make sure you know the dates, times and locations of all your examinations and allow plenty of time to travel.