I think you are trying to cast the wrong thing. You are trying to cast a character to a CameraManager. I think you may need to grab the controller and then the camera manager from it.
Well now I just feel like an idiot. Ha, it worked. Nicely done. You’re definitely right about the casting part. Well, I learned my lesson. Thanks a bunch.
APlayerController* MyPC = Cast<APlayerController>(Controller);
auto CameraManager = MyPC->PlayerCameraManager;
CameraManager->SetFOV(15.0f);