fuel guage missread

i had recently recieved a century on loan from a family member, they dont know what was done but they had some work done to it. now when it is on the full mark the guage is 1/8th over the full mark and is empty 1/8th before the E mark. how do i fix this? any help appreciated.

What year and model Century and what engine size?

95 buick century with 3.1 v6