Put a heat gun or good hair dryer on it.
Just did that with my new kydex holster for my CZ75B in .40 S&W. Made sure the pistol was unloaded, heated up the holster with the heat gun, jammed the pistol in and let the kydex cool down.
Oh yeah, my excuse, in the past, for ordering a new gun has been to buy magazines for it first. Then you need the pistol/rifle so you can use your new magazines.