TPMS needs to be reset so it has a baseline tire pressure to go by. First inflate the tire pressure where you want, then perform a reset. Look in the owner's manual for the instructions.
What vehicle is this procedure for?
I've had TPMS equipped vehicles for the past 15yrs or so and none of them required that.
Toyota requires this. Of course we don't know what OP has.
My toyota sensors on the scantool read quite a bit off from my reference gauge. But toyota is set to alarm at 80% of proper PSI, so, perhaps, the actual reported number isn't that accurate. I cannot pull up any particular tire or its PSI on the dashboard of my prii, only through the scan tool.
Toyota procedure is to double-check correct pressure then hit a button under the dash to set/reset.