As a result of such preparation, he will receive a pretty complete impression of what awaits him outside the doors of the medical office.
Usually the child asks if he will be painful during the procedure. The main thing here is by no means to deceive him and not say that there will be no pain, because he can generally stop trusting you after that. If you know that the child will be a little painful and unpleasant, you need to warn him about it. But immediately reassure him that it will only hurt a little, and therefore everything will pass very quickly.