In addition to these suggestions by Toffo and Swerve, if you are also having an issue during your turn-in…you might want to look into your brake balance. Put more to the rear.
To Toffo’s point, these are not great cars on Forza, yet, can do OK. Can you give us a little more info, at least the car and class, then, I can take a quick look at it myself.
So, you are getting oversteer? I have tuned both TT’s and an R8 with no oversteer so I’d have to see the build/tune and class to see where the problem may be mostly because it’s usually as PR kid said, awd’s usually have to be coerced to oversteer. Even if I can’t help, there’s a tuner out there that can and seeing the build and tune makes it a lot easier to diagnose a problem
To add to that, most of these guys will actually put your build and tune on a car, drive it, make the necessary adjustments and post back what they did to improve on it. I know this because they have done it for me.