PDF (adobe.com)

Reverse the direction of playback of a layer

When you reverse the direction at which a layer plays back, all keyframes for all properties on the selected layer also reverse order. The layer itself maintains its original In and Out points relative to the composition.

Note: For best results, precompose the layer and then reverse the layer inside the precomposition. For more information on this process, see About nesting and precomposing.
  1. In a Timeline panel, select the layer you want to reverse.
  2. Choose Layer > Time > Time-Reverse Layer, or press Ctrl+Alt+R (Windows) or Command+Option+R (Mac OS).