I double clicked on a layer and the preview only shows that layer. How do I transfer it?

Hi.

I think what you meant is that you're double-clicking on a symbol instance on stage.

If that's the case, you can select the layers inside of this symbol, right-click them, choose Copy Layers, go back to the main timeline, right-click again and choose Paste Layers.

Please let us know if this is what you need to do.

Regards,

JC