What would have to happen to be done to a plant oil to transform it into a trans-fat

The oil has to be subjected to a process called partial hydrogenation where hydrogen atoms are added to unsaturated fats such as oils. The process involves the use of heat in presence of hydrogen and certain metal catalysts which results in fats that are liquid at room temperature becoming solid. The change in physical state occurs because some unsaturated bonds become saturated i.e. fully hydrogenated and others are converted from cis arrangement to trans position creating straight solid molecules that pack together more solidly.