composition>save frame as>file

Go to the frame that you want to export so that it is shown in the Composition panel.
Do one of the following:
To render a single frame, choose Composition > Save Frame As > File. Adjust settings in the Render Queue panel if necessary, and then click Render.
To export a single frame as an Adobe Photoshop file with layers, choose Composition > Save Frame As > Photoshop Layers.