I just got a holster from them too, the "open top" with that reddish-brown color to it?
If so here's what I did & it seems to have worked for me.
I rubbed a
little neatsfoot oil in. (The leather was well filled with oil of some kind already & I didn't want to overdo it).
Then I used a hair dryer set on low flow & high heat to help the oil penetrate the leather evenly. To do this I put the holster back in the shipping box minus the packing & used the dryer to heat the box inside & contents for about 15 minutes to really soak the leather with heat all the way through.
Once that was done I shoved the pistol into a 1-gallon Ziploc bag, muzzle first, & wiggled it into the hot, oily holster. The purpose of the bag is to protect the finish from the hot oil, leather tanning leftovers & so on. Then I let it sit for 3 days.
Now its darn near a perfect fit, just firm enough grip to keep it in place but loose enough to allow for drawing without it slipping on the belt. I store the empty holster with a plastic (empty) pill container in the space where the cylinder would normally be, this keeps the shape in that area as well.