Probably not over written because backup file names (if left for defauts) include a date/time stamp in the filename itself. So you might be in luck!
Go into troubled course in edit mode. Pretend ... that's PRETEND (pardon my shouting) to restore the course.
When viewing that page, if course backups are present, you'll see them there and can download. Cancel the pretend restore.
Try above first ... other wise ... the last resort method involves query of DB for filenames (mdl_files table) that end with .mbz extension to acquire the contenthash value.
Then command line find of moodledata/filedir/ for a file by the name of that contenthash.
Then copying ... note that's copying ... the found contenthash named file in moodledata/filedir/xx/yy/contenthashnamed file to an area outside of Moodle and moodle data while also renaming the contenthashed name file to something Moodle restore would recognize as a valid backup file ... something like 'mybackup.mbz'.