First thing would be mindset. Always go in with a mindset that you will do well and that you'll ace your exam even if you may not think so because it may affect how you would answer the questions given.
Secondly, just remind yourself that you have done your best to study hard.
Thirdly, I would just suggest that if you have time before your exams, draw a mindmap that links all the concepts that you learnt so before the exams you can look through it to have an overview.
Lastly, when you have a few minutes before the exams, don't read through your notes because it will just make you more stressed. Take a few deep breaths. You can do it!
Hope this helps!
-Gabrielle