By default your render files will be in whichever location was set as your primary scratch disk.
If you select the unrendered clips on the timeline and right click you should see an option to reconnect media. This should show you online files, offline files and render files via 3 tabs top right. Select renders and it should list which renders are missing and the original location of those files.
You should then be able to locate that folder and relink your render files.
However if you are having trouble with this it may end up being just a quick to re-render depending on how many there are of course.