How do you tighten the battery mechanism to keep the hands from flopping? ?

I have a round battery wall clock and the battery and time gear housing just flops around when you move it. It will keep time when just resting, but when you try to hang it, the hands will stop moving properly. There is no nut on the face, or in back, to tighten. How do you tighten the mechanism to the back of the clock to stop the hands from flopping around?