If that's the option you selected when you imported it, then you need to assign an instance name to the FLVPlayback component inside the MovieClip and to the MovieClip as well. Use them to assign an event listener for the flv player to detect when it is done playing so you can start it playing again.
For the example shown below I have named them flvplayer and flvmc, respectively...
// in the timeline containing the MovieClip...
flvmc.flvplayer.addEventListener(Event.COMPLETE, playAgain);
function playAgain(evt:Event):void {
flvmc.flvplayer.play();
}
