Before you fight a Tyrannosaurus, choose a flat and open ground that doesn't have a lot of trees, as trees can be serves as obstacles from time to time, slopes are your greatest enemy while you're engaging a Tyrannosaurus as you'll likely to take trample damage by it, fighting it in flat terrain can greatly reduce the risk.

After you choose a perfect spot to attack, try to attack its rear, if it is chasing you, quickly move around and make the circle tighter until you reach its tail, after that keeps attacking it's tail and its ankle if possible while turning around with Tyrannosaurus at perfect synchrony

During the battle, aim the tail and thighs, ankles are also good but you might have risk taking trample damage, keep doing this for like 8~10 minutes and it will likely go down.

Congratulations! you just killed a Tyrannosaurus and ended its reign, now you're the new apex predator in hell creek! though that doesn't necessarily mean you're invincible, you still have to wary nearby environment.

Oh, forget to tell you one thing, Tyrannosaurus can sometimes being crafty, try to run away in the middle of battle, it only happens when its at low health, but be careful, as it might occasionally stop and try to turn around than kills you instantly before you know it! always stay alert while fighting the tyrant.

Even though I taught you how to kill a Tyrannosaurus, it's recommended to do that once you're Super Adult stage, and hope this will help you a lot, don't try that on realistic mode unless you have the confidence, either way, have fun hunting!