fuel gauge not right. how to fix on 1999 Cadillac DeVille

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
reads 16 or 17 gallons all the time. when it gets low, the low light does come on. how to fix.
(2) Answers
This happened on my 99 deville and my mechanic simply reset the computer by pushing a couple of buttons on the dash around the heater controls. I am not an expert, but if you can find which buttons to hit it is an easy fix.