Physics Can I reduse understeer and increase grip using AC Car Tuner app?

[hondapromx]

How Can I reduse understeer using AC Car Tuner app

 

[Tennisbiki]

My understanding is that AC Car Tuner app can be used to edit various ini files, including suspension.ini.
But if your problem is understeering, I would start with the existing setup options with wheelrate, ride height (rake for the car), camber, toe, damping, tire pressure. If those are not available then mess with suspension.ini. For me then, I would edit the setup.ini to allow me to adjust those parameters in game, in the pit.
What car are you driving or having this problem, and how much experience do you have with driving in AC?