Function refit_faces_as_one 

pub fn refit_faces_as_one(
    solid: &BrepSolid,
    face_ids: &[u64],
    kind: RefitSurfaceKind,
    tolerance: f64,
) -> Result<(BrepSolid, RefitReport), KernelRefusal>

Replace the faces face_ids of solid with one face on a surface of family kind fitted to them, within tolerance (maximum vertex residual, model units). See the module docs for the scope and the refusals.