A/How does a person reinstall a missing file on a Okuma OSP 5000 operating system from a floppy disk without deleting the whole machine file?
B/ How does a person make up a back file on the machine?
it depends on actual configuration. Paper tape (or simulators) is most common on OSP5000. Okuma is able to develop 3,5" installation media, if applicable.
what does it means "without deleting ..."? simple re-installation is quicker than replacement of file for these machines.
File can be replaced easily. Installation for this OSP means preparation of space (= memory partitioning)+ placing files where they belongs.