1) if you don't want to start over, there's an easy solution only for the files that have been moved.
You can type "Control + L" to mass edit the location fields. This will allow you to replace a string by another string.
2) if you've made too many changes and want to start over, you just have to delete your coollection file and scan your files again.
To delete your coollection file, select the menu "Help->Locate my coollection file", then close Coollector (necessary), then delete the file "MyCoollection.cool". When you'll launch Coollector again, a brand new coollection file will be created.
http://www.coollector.com/help.html#coollection