Sorry, it isnt an exam in the sense you can prepare for it. It is a medical. You cant have multiple attempts! However, if you have passed the class 2, have no significant medical history, are not colour blind and under 30 the risk of something being found is minimal
You cant pass by changing your lifestyle, but anyone looking at aviation for a career, where paying the mortgage depends on their medical, will presumably eat a sensible diet, not smoke, exercise and minimise alcohol.
Not sure what horror stories you have heard. The reality is the medical is simply a series of tests which most people pass
Good luck