HI Lillian…
As long as the original file still exists in the project (which I assume it does as you still have it’s audio in the sequence):
There is a Keyboard command you might have to map called: Match Frame (i set it to H)
1) Park you timeline cursor at the head of a clip where the Video has been removed on the timeline.
2) Select the Gap by clicking on it and hit the / key. This will Mark the duration of the gap.
3) Click the Audio Track label that contains the audio for the source.
4) Press The H (or whatever you mapped it to) key. This reloads the original clip into the source viewer and parks the playhead in the viewer to the “matched frame” of what you have on the timeline.
5) Clear all the in and out points in the viewer (G Key unless you’ve remapped it)
6) Press I to mark and in on the source viewer
7) Press . to perform an overlay edit back to the timeline.
You should now have your original source back on the timeline…
Hope that helps….
Alex