It's best to start a new thread, but since you're here...
Clicking the preview and clip tabs (top-left of the preview window) toggles between those modes, if that's what you have in mind.
To revert to the original clip, <ctrl-Z> (EDIT|UNDO) will step back through many prior changes.
Another approach might be to click the media clip, then the green (down) arrow and "place at cursor on new track." Or drag the media clip to the new track.
