Apple Final Cut Pro 6 - Manual (Page 492)

Chapter 10 Three-Point Editing 159
II
To use a replace edit to resync a video clip to an audio clip in another track:
1 In the Timeline, choose Mark > Clear In and Out (or press Option-X) to delete any
sequence In and Out points.
2 In the Timeline, find the audio cue you want to sync your video clip to, and position the
playhead there.
3 Make sure that the Source and Destination controls in the Timeline are set to the tracks
containing your video clip, and not your audio clip.
The video track should
be the only destination
track set.