When the tires reach the recommended tire pressure per the drivers side door placard (35 psi for 19") the light should go off. Either there is a problem with the sensor in the tire or the pressure gage you used is defective.
The reset process which is pretty easy in my opinion, relearns the postion of each sensor when the tires are rotated. Each sensor has a unique address sort of like a WiFi setup.
You may want to go through the reset (relearning) procedure to ensure that the correct tire position is indicated. If the tires were rotated and no one reset the positions, then the tire with the low air will not be in the postiton it indicates. You may be adding air to the incorrect tire.
So reset, adjust as needed and if the low pressure is still lit, bring it in for a check up.