The approach kinda depends upon the links to files ... the 'Start Here'.
Basically, all files uploaded to moodle reside in /moodledata/filedir/ but not by humanly recognizable names. So one might need to see the 'Start Here' link to see the humanly recognizable name, then use DB queries on the mdl_files table of the database for moodle for that humanly recognizable name to find the contenthash value.
Contenthash is a long series of letters/numbers but they do indicate the location of files in moodledata/filedir/
Example of contenthash: fsqwehwrgwf324asvwlwehr
Using above info, a file you need to find should be in /moodledata/filedir/fs/qw/ ... note the first 2 characters of contenthash is a subdirectory in moodledata/filedir/ ... the second two characters are a subdirectory of the first subdirectory. And in /moodledata/filedir/fs/qw/ is a file by the name of 'fsqwehwrgwf324asvwlwehr'.
Using OLD site backups to restore these sorts of individual course issues, is NOT the path to go. Can't restore only the pieces you need.
Using OLD course backups is more 'surgical' in that one could restore only the 'Start Here' resource into an existing course and thus one *might* be able to re-acquire the files 'Start Here' used to link to - depending upon if missing files were in the backup.
Server Linux? There is a command line thang one could install that has some commands to help deal with the file system called 'moosh' - https://moosh-online.com/ Might help.
'spirit of sharing', Ken