As said above, a soft holster is a ruined holster.
You can go to several holster manufacturer's websites and see what they recommend, but what I have found is to wet the holster well, wrap your gun in sandwich wrap to protect it, and then just stick the gun in it and let it dry slowly. Use a non-softening leather treatment like mentioned above afterwards and you should be GTG.
I like this stuff, it doesn't soften up the leather to where it loses it's strength or shape:
https://www.obenaufs.com/index.php?r...&product_id=72
HTH