Hi Adorra,
My advice is to gather direct feedback from trusted friends and relatives who have undergone a successful colonoscopy on whom to consider as your endoscopist. In this era of fake news and social media marketing, it is even more important now to distil reviews accurately.
When you speak to your endoscopist, remember that you are not obliged to undergo the procedure unless you are comfortable with the doctor and accept the risks involved with the procedure.
Finding a good doctor for your colonoscopy in Singapore should not be that complicated!