There are a few ways to tranq a T Rex, but the most common is to use a tranquilizer dart. To do this, you will need a rifle that is powerful enough to shoot the dart into the T Rex, and it must be loaded with the right kind of tranquilizer. Once you have your rifle and dart ready, aim for the T Rex's head and neck area, and shoot the dart. The T Rex will likely become drowsy within minutes, making it easier to transport or handle.