Not an answer per se, but...
Some stretching / pressing might help, but I am reluctant. Some kind of oily "massage" might help also.
Please note that if the leather is "floating" (not glued to a non-stretch reinforcing material) you can end up with curls instead of wrinkles - which would be quite bad.
As a matter of fact, my initial reaction (before reading the text) was that the problem was in the upper part of the picture. So, if you wear that wallet in the rear pocket of your pants for a while, you should get your desired effect without any additional effort (besides carrying it with you).
If I were you, I would just embrace the new personality of the wallet, rather than risk destroying it. To anyone else besides you, the wallet looks exactly as it was supposed to look.