Anyone who is new at the track and is complaining of understeer and destroying tires is not talking about understeer in the sense of suspension and balance. This is related to overdriving and asking too much of the front tires.
Tire pressures won't fix this...slowing down and being smoother is the only way. Adding extra pressure to fix this is decreasing traction which, if not corrected, exacerbates the problem.
I recommend starting at 35psi if temps are below 70. Less if it's hotter. I also like to target about 38/39 psi.
OP- just change your brake fluid and start with at least 50% tires and brakes.
Check Patroon, Boston, DelVal, or NJ chapter for HPDE events.