Please see: https://docs.moodle.org/26/en/File_system_repository
DO NOT mess with filedir at all.
Basically one must create a 'repository' directory in moodledata
Then create one more folder inside 'repository' where you will upload the .mbz backups. Call that folder 'backups2restore' (note lower case - NO spaces name). There should be no doubt later the purpose of that folder/directory.
Enable the File System Repository at desired level (system wide ok)
Suggest creating a category called 'restores' (hidden and only available to sys admin). Create a course called 'restores' in that category. Only need 1 section, no news or other blocks in that course. In the 'restores' course turn on file system repo and use that to restore the courses to other categories in your Moodle.
'spirit of sharing', Ken