Hi Mehnaz, this tutorial will help you get those wrinkles out - https://www.sheknows.com/living/articles/1069141/how-to-get-wrinkles-out-of-leather-jackets/
Buy a leather restorer or saddle soap to feed the leather.
Here's a link with 3 things to try:
Are the wrinkles due to the leather being cracked, dried out, or being stored for a long time folded? Please post a picture of the the jacket so that we can see what you are starting with.
Hello Mehnaz, hope these help you out, one method is to steam it in your bathroom with hot shower steam or carefully iron as per this video
Here is helpful video: https://www.youtube.com/watch?v=N9xz26FgK4I
Hang in the shower and let the steam ease the wrinkles out.
Iron it from the inside on low
I keep mine on a wood hanger with wide "shoulders" .