1997 4.3 blazer 02 sencors

what 02 sensor do i replace the code says 0146 bank 1 sencor 3
but my blazer only has 2 sensors one in front of cat and one behind so what one is bad or do i change both.

You should also have one on each exhaust pipe near the exhaust manifolds.

ok theres 3 one on each side by manifolds, and one back by the cat so what sensor do i replace,