In modern esthetic view, oval face is a preferred face profile.  The lower facial profile in front view is determined by bony structure (lower jaw, or mandible) and masseter muscle which is attached on lateral side of lower jaw.

There are two ways of treating square face.  One is bone surgery, which shaves the mandible angle.  The other is Botox injection to masseter muscle to shrink the thickness of masseter.  Below right show the result of mandible angle reduction.

Botox injection is a less invasive way to slim face.  Botox can reduce the thickness of masseter muscle.  The thicker the masseter muscle, the higher the dose.  The effect of slimming face is more obvious in people with thick muscle.  But the effect lasts about 6 months.  Below show the location of masseter and the result after Botox injection (below right is after injection) .

Bone surgery can correct people with prominent zygoma.  The other way is fat injection into depressed cheek or temple.  It is less injection and less risky.  Below show the result of fat injection.