meat - congrats on both counts (job & machete)
Cap'n - good luck.
Clich - so long as the leather hasn't been waxed/sealed, you can soak and shape it.
I use warm water - submerge the sheath until it stops bubbling, then wrap it in a towel for half an hour to let the water soak through all the leather. Wrap knife in "press-n-seal", put it in the sheath, and form it by hand or with a tool (antler, bone, wooden stirring spoon, etc - whatever is close at hand that won't cut the wet leather)
when I'm done forming, I put the entire mess (knife still in sheath) in a window and leave it for a full day to dry out.
after about 3 hours, the leather will be dry enough to remove the knife - but not "dry". After it's all dried out give it a coat of oil (neatsfoot is good, ball glove conditioner is OK) inside and out, let sit overnight again, then seal it. (I like sno-seal)