Control Z = undo. You can undo multiple times, based on prefs (I think).

Ctrl+z works fine. Way to go.
But if what you want is go back to a "normal" frame into the track motion, go to the top of the box and click the arrow then choose "reset to normal". You then get back to the original frame.
You can also reset the "keys" or delete some of them: place the cursor (arrow) on the small tilted square on the timeline "reproduction" that's at the bottom of the track motion window then, when it's switched on (you'll notice a change on this actual square)you can press "delete" or go further down in the same window and click on the tilted square with a minus sing (-) in it. Pop! the key's gone...

Duh... if you look closely you'll see a minu sign in most key framed events. click on the little diamond in the FX control window timeline, then the minus key for any keyframe you don't want and its gone. The undo key will work too for most things.