I had a crash on my computer.
Fortunately I had backups of all my photos: YEAH!
Unfortunately I wasn't really good about how I stored them and where. In short, good back up habits; bad backup file management. - BOO!
I have created a copy of all my backups to one folder tree now and am ready to match the photos that are stored in LR (but file can't be found).
I have found that if I search for a file and locate that file and click on the find nearby files it will find "some" and map them. But what I don't see is a way to do this once for all photos already in LR - a one click, find them all, wizard of sorts.
Thanks for any suggestions.
If you have so many images to remapping in Lightroom 6 catalog and not done much of editing, then you can simply create a new catalog and re-import all the images from their original location.
For remapping the Images you have in the existing catalog you can refer the link : How to find missing photos in Photoshop Lightroom
Let us know if that helps.