Insert a drinking straw into the narrow fabric shape (or casing), pushing the end of the straw against the inside of the closed end of the fabric shape.  Hold the blunt end of a small crochet/knitting needle or skewer against the outside of the fabric's closed end. Gently push the needle / skewer and closed end of the fabric shape into the straw, slowly edging the sides of fabric shape up and over the needle / skewer until your fabric shape is turned out.  Now you are ready to stuff it. To do this, use either your needle / skewer (I actually prefer my long nosed surgical tweezers) to push in only small amounts of stuffing at a time. If you try to push in large pieces of stuffing, you will end up with lots of spaces and lumps. 

There you go. I hope this helps! 
​Margeaux