I'll try to get some pics tomorrow, but it should be pretty easy to explain.
1. Cut the "top strap" part off the holster and unsnap the other half of it from the outer side of the holster - the top strap just gets in the way and in fact could present a safety risk if you have a pistol with no manual safety.
2. The Crosman has a few velcro pieces to create a belt loop. Take the two small horizontal pieces and fold them so that they are UNDER, not over the covering (vertical) velcro piece like they would normally be.
3. Apply pants & belt
4. Place the holster inside pants, with the large velcro flap in between pants and belt. This holds the holster in place and prevents the gun from slipping down.
This works great for right-hand small of back draw. It also works, albeit not necessarily very well, as a left-hand belly draw. I'm not sure if there's a good way to make it a right-hand IWB, but there are some pretty cheap generic IWBs that will do the job just as well if not better.
These Crosman holsters are darn nifty though, my wife uses one (sans top strap) to carry her EAA Windicator revolver in an OWB configuration and the retention is surprisingly good without making it too hard to draw.