Ever since changing the original wheels (19") to 22" every once in a while after driving for a few minutes in normal driving, right when I turn off the ignition, the -5 inflate warning comes up.

Only after turning off the ignition and only in the front tires. The pressure is a little off on the dash but fine with a tire pressure stick thingy.

To fix the warning on the dash, I go to Adjust - Winter tires and then select 20". Is there another way to reset this?

Plus, why is the dash off compared to my pressure thingy?

TIA.

sounds like a glitch, I would have the dealer check it out. I switch from 19's with snow tires to 21's with summer ones twice a year and as long as I toggle between the 2 different settings on the screen I've had no problems

What should be the ideal pressure at 22"? Right now I have it set at 40 PSI according to my pressure gauge.

Sounds like a tire sensor issue perhaps, from the sensor inside a wheel.