I would use a file manager to copy the files you need into your directory. So Lr can use them without changing the infos. Another way would be to copy your files - so too with your file manager - into another folder with a new name.
Nothing works. If I move files manually into desired folder or new folder or restore them into folder from which I deleted them, Lr see them, but does not allow me to develop them showing message "file could not be found".
The only solution was to re-name all files manually (there were few hundreds of them - it took me one hour!!!). After that I was able to import them and start developing.
Should working with Lr be so painful?
I'm sorry that you had to struggle with it in this circumstantially way. It's a pity, you didn't ask me earlier, because there are interesting programs which can handle this "rename" work. Some days before I gave a hint to one of them an admin here deleted it. So please use our other friend Google to find it.
... and please remind, we here in the forum are users like you, not Adobe's employees. And so what concerns your "Should working with Lr be so painful?" please have a look at https://www.adobe.com/cfusion/mmform/index.cfm?name=wishform, where you will find this: "Use this form to request new features or suggest modifications to existing features."
If the files were still on the camera memory card, the most straight-forward thing would have been to use LR to remove them from the library, and delete them from where they’d been copied, then reimport them specifying the correction location.
The initial mistake was not using LR to remove the errant import, and going behind LR’s back and using the OS.
Since you deleted them from the hard-disk but didn’t delete them from LR, LR could not reimport them as they were duplicates. Still the only thing you needed to do was remove them from LR so then LR wouldn’t think they were duplicates, and you’d be allowed to reimport them.
The suggestion to merely use the OS to move them to where you wanted was fine if you didn’t use the LR import to rename them as you imported. Since you apparently had, that required hand-renaming. Still what you should have done was remove them from LR and start over with the import.
And how I can remove the errant import using LR? Being completely new to LR I still struggle to locate all its buttons.
Here is an Adobe help page about doing things with folders including moving which is probably all you really had to do in the first place, if the images were imported and named correctly and only were in the wrong folder: