You will see a blue building on the side of the road opposite the gate of the medical college.
There is a big sign "STD clinic" on it.
Go into that building and go up to the third floor. There is a sign telling you how to apply for a health certificate.
First take photos, then internal medicine, chest X-ray, blood test, and finally take a book and a paper and leave. Just go to the second floor and get a health certificate in three days.