One technique you can try is washing your leather garment in the washing machine using the gentle cycle. Adding lots of liquid fabric softener is an option. This will agitate the leather, and possibly remove extra dye. After that, you can put it in the dryer without heat and let it tumble around (you might want to put it in a pillowcase or add towels).
You can also just do the dryer on its own, without heat, to help agitate and soften the leather. (Heat will make leather shrink.)
Wearing It Wet
Some suggest getting the garment wet or very damp, and then allowing it to dry. One option is to wear it while damp, or to let it dry while while wearing it, as this will conform the garment to your body and create wrinkles that may remain. Just remember to keep the garment out of the heat, because it may shrink.
While the garment is wet, roll the leather into a tight roll or series of folds. This will create permanent wrinkles and creases.
One costume designer soaked a leather jacket in “the juice of oranges and lemons” in order to give it a softer, worn-in look. The citric acids break down some of the proteins in the leather.