I would apply a generous application of leather treatment (bee’s wax, etc.) and either stick them out in the sun a hot summer’s day or use a blow dryer to heat the “wax” and let it soak into the leather. Then wear them around.
What I do, here in Montana, is pick a hot July or August day. Generously apply the “wax” and let it set and soak in for any hour or so (I keep an eye on them, as to not dry them out). The side of the boot that is facing the direct sunlight will melt and soak in first, so I rotate the boots until it have rotated them 360 degrees. You would be amazed how quickly the “wax” soaks into the leather in the hot sun. I buy my “wax” from Schnee’s located in Bozeman. I know Kenetrek sells their version, as well. Both good products.
You can apply one day and go on a hike the next, repeat if necessary.
Good luck.