Clean the leather chair using a pH neutral foam leather cleanser that is water-based. Wash the chair to remove all dirt and oils. Dry with a towel.
Apply a pigskin leather protector. This prevents oils from accumulating on the leather. Moisten a rag and wipe the chair down with water after the protector dries. Water rehydrates leather. You can also use a leather hydrator product. Move the chair out of a sunny location, as constant sunlight will fade and dry out the leather.
Turn on a hair dryer and move it across the pigskin seat. Place one hand under the leather. If your hand becomes too hot, the leather is too hot. Move the dryer away and place the metal baking pan on the leather. The pan will act as a heat sink and draw the heat off quickly.
Allow the leather to cool and heat it up again. The fibers within the leather will shrink causing the seat to tighten. Wipe the leather with a water-moistened rag when you are finished. The chair should be cleaned, protected and rehydrated regularly. Shrink the seat two or three times over a month until the seat is as tight as you want. Reshrink when you notice it starting to sag again.