You need to make an appointment with a gastroenterologist or a doctor at the Gastrointestinal Endoscopy Center to have a colonoscopy. Before the colonoscopy, you need to prepare your intestines by drinking laxatives and eliminating all the stool from your intestines before you can insert a tube through the anus to check whether there are any lesions in the intestinal mucosa. Colonoscopy is more complicated than gastroscopy, so it is not always possible to perform it. Basically, it is limited to the afternoon of every day, and the number of patients is usually limited, so you should consult with the relevant department of the hospital you are visiting.