Is it possible to use .xlr files with LibreOffice? It appears I can’t edit them.
(Removed OP’s excuse for bad spelling after editing :))
.XLR files are not LibreOffice files. They are Microsoft Works file (the little brother of Office) which is no longer produced. A quick search in Google revealed that some Excel versions can open them. If you have a Office 2010 Starter (it was free) you can try it there.
I checked an older version of LO 3.6.6 and it was not in the list there.
A return question: can you open it in LO but not edit it? If so save the open file to a .ODT (calc) file and work with it.