Heat guns work, but damage the leather structure so you can’t repeatedly do the same area… If you hold them in place too long you can burn the leather and they will wreck any fabric or pu side borders. As this is a diy job, you will learn how much heat is too much by destroying the seat covers. If the seats get creasing or dents from being folded, they will recover with time and a bit of massaging. Steam also gets wrinkles out with less risk to the leather. Try light, quick application of a steam iron through a damp cloth. Don’t hold it still or press it hard into the seat.