Unlace it, open it up a bit and let it warm under the sun for sometime.
wrap your hands with gauze to keep the sweat off the inside of the leather just like wearing socks inside athletic shoes then air them out when done
Hopefully you're wearing wraps already. If not wear wraps. Then after every training session air them up, hang them up somewhere. If you kept the little sachet with the powder in it, leave that in them, because that sucks up moisture.
You can tape your hand before sticking you hand in it, to catch the sweat. Rubber gloves?
I know there is going to be a little smell, but what can I do to keep my boxing gloves from smelling like something died in them? Cleaning tips??