you can't - flash does not have an image warp feature - you
would have to do 1 of 2 things:
Trace Bitmap the image to convert it to vectors - then use
Free transform tool > Envelope or Distort
Bend the image in P'shop and then import into flash.
If you need to bend the image as an animation - then flash is
not your tool - i would highly
recommend Animae Studio (www.e-frontier.com) for this (I use
it all the time). It supports IK
(Bones) and Image Warp - then export as Quicktime and Import
You can bend and warp vector images with The Tab
(www.the-tab.com), and export them as Flash movies. It also has
several effects borrowed from Illustrator and from higher end
animation programs that are not available in Flash, such as
textured lines. It's a very cool animation program, though the
interface is very different than anything you're used to.