Renamed optional labs and they all stopped working! Can anyone fix it, please!?

We can’t fix it for you, but you can fix it for yourself. Please see this thread, which is from DLS, but the same “Lab Help → Get Latest Version” method will work for MLS as well. See the section about the 404 error case. That will get you a clean copy that will open from the normal “Work in Browser” link. Then you can click “File → Open” from the clean notebook and rename your saved copies back to the standard name, if they contain any completed work.

If you want to save the notebooks to your local computer, there’s a topic about that on the DLS FAQ Thread. There are some topics there which are specific to DLS, but a lot of the items are generally applicable. It might be worth taking a quick scan through there just to be aware of what is covered.