Generally what Rod said will do the job.
A couple of things though, most epoxy resin starts to deteriorate if subjected to temperatures in excess of 70 degrees centigrade and leather that is subjected to extremely hot water will form very easily, but you will wash a lot of the natural oils from the leather, later it will become very hard and inflexible unless you "feed" the leather on a regular basis, drying it out rapidly will have the same effect.
Other suggestions for tools to form the leather are a spoon (it doesn't have to be one you have carved
) or a modelling tool or even a pen.
When I wet form I don't use hot water, I use luke warm / tepid water, I don't speed up the drying process either by using an airing cupboard or sitting things on the heater. The results are very good. This is a picture that I have borrowed from another thread, it shows a knife with sheath and a possibles pouch, the sheath didn't require a lot of forming, but look at the possibles pouch.
I have a picture of a sheat hfor my F1 about somewhere which I'll dig out, also be aware that different types of leather have different properties and form better or worse than others (German Half Tanned is probably one of the best).