Reversing an animation

I have built an animation of a knob using several still images in the animation builder. I have the knob on a page and start it via an action on the animation image ( on mouse click toggle play mode of this object) It works fine to turn the animation on/off. What I would like to di is setup another action that says something like on right mouse click, reverse the direction of the animation so the knob rotates in the opposite direction. Does anyone know how to do this?

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