i really need to sort out the creasing in a trench coat, though i do think my problem is caused by another crease being present, i want to know how to add a crease if need be
Leather doesn’t react well to heat. It dries the fiber and can cause cracking later in the leather’s life.
The traditional method of creasing leather follows:
Fold the leather along the crease line against a hard surface. Pound the leather on the crease line with a rubber mallet, or, for better results, with a wood block that has rounded edges.
If you are not terribly concerned with the ultimate life of the leather, you can try steam heat from your iron on an inconspicuous place. If it does not stain or leave unsightly marks, you may use it to add a crease. But be forwarned, that the leather may show more wear at this point in the future.