Baby powder is a good short term solution. To really get it to fit you will need a dummy gun, or wrap yours in saran wrap. Then soak the holster in hot water till the bubbles stop comming out of the leather. Place the dummy gun into the holster and wear it till the holster is dry, usually about 2 days.
Holster will be broken in properly, and no more squeaks. Just before it gets totally dry, saddle soap it well and apply 100% neatsfoot oil. Put gun back in and wear another day.
The leather is vegetable tanned skirting leather (sometimes called molding leather). Properly done, this will not ruin even the finest leather. I have done this many times with everything from combat boots to $2000 saddles. Don't do this with chrome tanned leather. Chrome tanned leather is not used on holsters, it would rust your gun in nothing flat.
Good luck.