This is how I treat wet leather.
1) Pick up a glycerine bar or saddle soap,
work as much of it into the leather as possible.
2) When almost dry, soak with Leather New.
3) let it dry then work in as much tree wax as possible, heat with a blow dryer and rub it to a polish.
This method just worked very well with a sheath that had been in water for over 2 years. It does not look new, but acceptable as possible.